1 ===================== 1 =====================
2 DRM Memory Management 2 DRM Memory Management
3 ===================== 3 =====================
4 4
5 Modern Linux systems require large amount of g 5 Modern Linux systems require large amount of graphics memory to store
6 frame buffers, textures, vertices and other gr 6 frame buffers, textures, vertices and other graphics-related data. Given
7 the very dynamic nature of many of that data, 7 the very dynamic nature of many of that data, managing graphics memory
8 efficiently is thus crucial for the graphics s 8 efficiently is thus crucial for the graphics stack and plays a central
9 role in the DRM infrastructure. 9 role in the DRM infrastructure.
10 10
11 The DRM core includes two memory managers, nam !! 11 The DRM core includes two memory managers, namely Translation Table Maps
12 (TTM) and Graphics Execution Manager (GEM). TT 12 (TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
13 manager to be developed and tried to be a one- 13 manager to be developed and tried to be a one-size-fits-them all
14 solution. It provides a single userspace API t 14 solution. It provides a single userspace API to accommodate the need of
15 all hardware, supporting both Unified Memory A 15 all hardware, supporting both Unified Memory Architecture (UMA) devices
16 and devices with dedicated video RAM (i.e. mos 16 and devices with dedicated video RAM (i.e. most discrete video cards).
17 This resulted in a large, complex piece of cod 17 This resulted in a large, complex piece of code that turned out to be
18 hard to use for driver development. 18 hard to use for driver development.
19 19
20 GEM started as an Intel-sponsored project in r 20 GEM started as an Intel-sponsored project in reaction to TTM's
21 complexity. Its design philosophy is completel 21 complexity. Its design philosophy is completely different: instead of
22 providing a solution to every graphics memory- 22 providing a solution to every graphics memory-related problems, GEM
23 identified common code between drivers and cre 23 identified common code between drivers and created a support library to
24 share it. GEM has simpler initialization and e 24 share it. GEM has simpler initialization and execution requirements than
25 TTM, but has no video RAM management capabilit 25 TTM, but has no video RAM management capabilities and is thus limited to
26 UMA devices. 26 UMA devices.
27 27
28 The Translation Table Manager (TTM) 28 The Translation Table Manager (TTM)
29 =================================== 29 ===================================
30 30
31 .. kernel-doc:: drivers/gpu/drm/ttm/ttm_module !! 31 TTM design background and information belongs here.
32 :doc: TTM <<
33 32
34 .. kernel-doc:: include/drm/ttm/ttm_caching.h !! 33 TTM initialization
35 :internal: !! 34 ------------------
36 <<
37 TTM device object reference <<
38 --------------------------- <<
39 <<
40 .. kernel-doc:: include/drm/ttm/ttm_device.h <<
41 :internal: <<
42 <<
43 .. kernel-doc:: drivers/gpu/drm/ttm/ttm_device <<
44 :export: <<
45 <<
46 TTM resource placement reference <<
47 -------------------------------- <<
48 <<
49 .. kernel-doc:: include/drm/ttm/ttm_placement. <<
50 :internal: <<
51 <<
52 TTM resource object reference <<
53 ----------------------------- <<
54 35
55 .. kernel-doc:: include/drm/ttm/ttm_resource.h !! 36 **Warning**
56 :internal: !! 37 This section is outdated.
57 38
58 .. kernel-doc:: drivers/gpu/drm/ttm/ttm_resour !! 39 Drivers wishing to support TTM must pass a filled :c:type:`ttm_bo_driver
59 :export: !! 40 <ttm_bo_driver>` structure to ttm_device_init, together with an
>> 41 initialized global reference to the memory manager. The ttm_bo_driver
>> 42 structure contains several fields with function pointers for
>> 43 initializing the TTM, allocating and freeing memory, waiting for command
>> 44 completion and fence synchronization, and memory migration.
60 45
61 TTM TT object reference !! 46 The :c:type:`struct drm_global_reference <drm_global_reference>` is made
62 ----------------------- !! 47 up of several fields:
63 48
64 .. kernel-doc:: include/drm/ttm/ttm_tt.h !! 49 .. code-block:: c
65 :internal: <<
66 <<
67 .. kernel-doc:: drivers/gpu/drm/ttm/ttm_tt.c <<
68 :export: <<
69 50
70 TTM page pool reference !! 51 struct drm_global_reference {
71 ----------------------- !! 52 enum ttm_global_types global_type;
>> 53 size_t size;
>> 54 void *object;
>> 55 int (*init) (struct drm_global_reference *);
>> 56 void (*release) (struct drm_global_reference *);
>> 57 };
>> 58
>> 59
>> 60 There should be one global reference structure for your memory manager
>> 61 as a whole, and there will be others for each object created by the
>> 62 memory manager at runtime. Your global TTM should have a type of
>> 63 TTM_GLOBAL_TTM_MEM. The size field for the global object should be
>> 64 sizeof(struct ttm_mem_global), and the init and release hooks should
>> 65 point at your driver-specific init and release routines, which probably
>> 66 eventually call ttm_mem_global_init and ttm_mem_global_release,
>> 67 respectively.
72 68
73 .. kernel-doc:: include/drm/ttm/ttm_pool.h !! 69 Once your global TTM accounting structure is set up and initialized by
74 :internal: !! 70 calling ttm_global_item_ref() on it, you need to create a buffer
>> 71 object TTM to provide a pool for buffer object allocation by clients and
>> 72 the kernel itself. The type of this object should be
>> 73 TTM_GLOBAL_TTM_BO, and its size should be sizeof(struct
>> 74 ttm_bo_global). Again, driver-specific init and release functions may
>> 75 be provided, likely eventually calling ttm_bo_global_ref_init() and
>> 76 ttm_bo_global_ref_release(), respectively. Also, like the previous
>> 77 object, ttm_global_item_ref() is used to create an initial reference
>> 78 count for the TTM, which will call your initialization function.
75 79
76 .. kernel-doc:: drivers/gpu/drm/ttm/ttm_pool.c !! 80 See the radeon_ttm.c file for an example of usage.
77 :export: <<
78 81
79 The Graphics Execution Manager (GEM) 82 The Graphics Execution Manager (GEM)
80 ==================================== 83 ====================================
81 84
82 The GEM design approach has resulted in a memo 85 The GEM design approach has resulted in a memory manager that doesn't
83 provide full coverage of all (or even all comm 86 provide full coverage of all (or even all common) use cases in its
84 userspace or kernel API. GEM exposes a set of 87 userspace or kernel API. GEM exposes a set of standard memory-related
85 operations to userspace and a set of helper fu 88 operations to userspace and a set of helper functions to drivers, and
86 let drivers implement hardware-specific operat 89 let drivers implement hardware-specific operations with their own
87 private API. 90 private API.
88 91
89 The GEM userspace API is described in the `GEM 92 The GEM userspace API is described in the `GEM - the Graphics Execution
90 Manager <http://lwn.net/Articles/283798/>`__ a 93 Manager <http://lwn.net/Articles/283798/>`__ article on LWN. While
91 slightly outdated, the document provides a goo 94 slightly outdated, the document provides a good overview of the GEM API
92 principles. Buffer allocation and read and wri 95 principles. Buffer allocation and read and write operations, described
93 as part of the common GEM API, are currently i 96 as part of the common GEM API, are currently implemented using
94 driver-specific ioctls. 97 driver-specific ioctls.
95 98
96 GEM is data-agnostic. It manages abstract buff 99 GEM is data-agnostic. It manages abstract buffer objects without knowing
97 what individual buffers contain. APIs that req 100 what individual buffers contain. APIs that require knowledge of buffer
98 contents or purpose, such as buffer allocation 101 contents or purpose, such as buffer allocation or synchronization
99 primitives, are thus outside of the scope of G 102 primitives, are thus outside of the scope of GEM and must be implemented
100 using driver-specific ioctls. 103 using driver-specific ioctls.
101 104
102 On a fundamental level, GEM involves several o 105 On a fundamental level, GEM involves several operations:
103 106
104 - Memory allocation and freeing 107 - Memory allocation and freeing
105 - Command execution 108 - Command execution
106 - Aperture management at command execution ti 109 - Aperture management at command execution time
107 110
108 Buffer object allocation is relatively straigh 111 Buffer object allocation is relatively straightforward and largely
109 provided by Linux's shmem layer, which provide 112 provided by Linux's shmem layer, which provides memory to back each
110 object. 113 object.
111 114
112 Device-specific operations, such as command ex 115 Device-specific operations, such as command execution, pinning, buffer
113 read & write, mapping, and domain ownership tr 116 read & write, mapping, and domain ownership transfers are left to
114 driver-specific ioctls. 117 driver-specific ioctls.
115 118
116 GEM Initialization 119 GEM Initialization
117 ------------------ 120 ------------------
118 121
119 Drivers that use GEM must set the DRIVER_GEM b 122 Drivers that use GEM must set the DRIVER_GEM bit in the struct
120 :c:type:`struct drm_driver <drm_driver>` drive 123 :c:type:`struct drm_driver <drm_driver>` driver_features
121 field. The DRM core will then automatically in 124 field. The DRM core will then automatically initialize the GEM core
122 before calling the load operation. Behind the 125 before calling the load operation. Behind the scene, this will create a
123 DRM Memory Manager object which provides an ad 126 DRM Memory Manager object which provides an address space pool for
124 object allocation. 127 object allocation.
125 128
126 In a KMS configuration, drivers need to alloca 129 In a KMS configuration, drivers need to allocate and initialize a
127 command ring buffer following core GEM initial 130 command ring buffer following core GEM initialization if required by the
128 hardware. UMA devices usually have what is cal 131 hardware. UMA devices usually have what is called a "stolen" memory
129 region, which provides space for the initial f 132 region, which provides space for the initial framebuffer and large,
130 contiguous memory regions required by the devi 133 contiguous memory regions required by the device. This space is
131 typically not managed by GEM, and must be init 134 typically not managed by GEM, and must be initialized separately into
132 its own DRM MM object. 135 its own DRM MM object.
133 136
134 GEM Objects Creation 137 GEM Objects Creation
135 -------------------- 138 --------------------
136 139
137 GEM splits creation of GEM objects and allocat 140 GEM splits creation of GEM objects and allocation of the memory that
138 backs them in two distinct operations. 141 backs them in two distinct operations.
139 142
140 GEM objects are represented by an instance of 143 GEM objects are represented by an instance of struct :c:type:`struct
141 drm_gem_object <drm_gem_object>`. Drivers usua 144 drm_gem_object <drm_gem_object>`. Drivers usually need to
142 extend GEM objects with private information an 145 extend GEM objects with private information and thus create a
143 driver-specific GEM object structure type that 146 driver-specific GEM object structure type that embeds an instance of
144 struct :c:type:`struct drm_gem_object <drm_gem 147 struct :c:type:`struct drm_gem_object <drm_gem_object>`.
145 148
146 To create a GEM object, a driver allocates mem 149 To create a GEM object, a driver allocates memory for an instance of its
147 specific GEM object type and initializes the e 150 specific GEM object type and initializes the embedded struct
148 :c:type:`struct drm_gem_object <drm_gem_object 151 :c:type:`struct drm_gem_object <drm_gem_object>` with a call
149 to drm_gem_object_init(). The function takes a 152 to drm_gem_object_init(). The function takes a pointer
150 to the DRM device, a pointer to the GEM object 153 to the DRM device, a pointer to the GEM object and the buffer object
151 size in bytes. 154 size in bytes.
152 155
153 GEM uses shmem to allocate anonymous pageable 156 GEM uses shmem to allocate anonymous pageable memory.
154 drm_gem_object_init() will create an shmfs fil 157 drm_gem_object_init() will create an shmfs file of the
155 requested size and store it into the struct :c 158 requested size and store it into the struct :c:type:`struct
156 drm_gem_object <drm_gem_object>` filp field. T 159 drm_gem_object <drm_gem_object>` filp field. The memory is
157 used as either main storage for the object whe 160 used as either main storage for the object when the graphics hardware
158 uses system memory directly or as a backing st 161 uses system memory directly or as a backing store otherwise.
159 162
160 Drivers are responsible for the actual physica 163 Drivers are responsible for the actual physical pages allocation by
161 calling shmem_read_mapping_page_gfp() for each 164 calling shmem_read_mapping_page_gfp() for each page.
162 Note that they can decide to allocate pages wh 165 Note that they can decide to allocate pages when initializing the GEM
163 object, or to delay allocation until the memor 166 object, or to delay allocation until the memory is needed (for instance
164 when a page fault occurs as a result of a user 167 when a page fault occurs as a result of a userspace memory access or
165 when the driver needs to start a DMA transfer 168 when the driver needs to start a DMA transfer involving the memory).
166 169
167 Anonymous pageable memory allocation is not al 170 Anonymous pageable memory allocation is not always desired, for instance
168 when the hardware requires physically contiguo 171 when the hardware requires physically contiguous system memory as is
169 often the case in embedded devices. Drivers ca 172 often the case in embedded devices. Drivers can create GEM objects with
170 no shmfs backing (called private GEM objects) 173 no shmfs backing (called private GEM objects) by initializing them with a call
171 to drm_gem_private_object_init() instead of dr 174 to drm_gem_private_object_init() instead of drm_gem_object_init(). Storage for
172 private GEM objects must be managed by drivers 175 private GEM objects must be managed by drivers.
173 176
174 GEM Objects Lifetime 177 GEM Objects Lifetime
175 -------------------- 178 --------------------
176 179
177 All GEM objects are reference-counted by the G 180 All GEM objects are reference-counted by the GEM core. References can be
178 acquired and release by calling drm_gem_object 181 acquired and release by calling drm_gem_object_get() and drm_gem_object_put()
179 respectively. 182 respectively.
180 183
181 When the last reference to a GEM object is rel 184 When the last reference to a GEM object is released the GEM core calls
182 the :c:type:`struct drm_gem_object_funcs <gem_ 185 the :c:type:`struct drm_gem_object_funcs <gem_object_funcs>` free
183 operation. That operation is mandatory for GEM 186 operation. That operation is mandatory for GEM-enabled drivers and must
184 free the GEM object and all associated resourc 187 free the GEM object and all associated resources.
185 188
186 void (\*free) (struct drm_gem_object \*obj); D 189 void (\*free) (struct drm_gem_object \*obj); Drivers are
187 responsible for freeing all GEM object resourc 190 responsible for freeing all GEM object resources. This includes the
188 resources created by the GEM core, which need 191 resources created by the GEM core, which need to be released with
189 drm_gem_object_release(). 192 drm_gem_object_release().
190 193
191 GEM Objects Naming 194 GEM Objects Naming
192 ------------------ 195 ------------------
193 196
194 Communication between userspace and the kernel 197 Communication between userspace and the kernel refers to GEM objects
195 using local handles, global names or, more rec 198 using local handles, global names or, more recently, file descriptors.
196 All of those are 32-bit integer values; the us 199 All of those are 32-bit integer values; the usual Linux kernel limits
197 apply to the file descriptors. 200 apply to the file descriptors.
198 201
199 GEM handles are local to a DRM file. Applicati 202 GEM handles are local to a DRM file. Applications get a handle to a GEM
200 object through a driver-specific ioctl, and ca 203 object through a driver-specific ioctl, and can use that handle to refer
201 to the GEM object in other standard or driver- 204 to the GEM object in other standard or driver-specific ioctls. Closing a
202 DRM file handle frees all its GEM handles and 205 DRM file handle frees all its GEM handles and dereferences the
203 associated GEM objects. 206 associated GEM objects.
204 207
205 To create a handle for a GEM object drivers ca 208 To create a handle for a GEM object drivers call drm_gem_handle_create(). The
206 function takes a pointer to the DRM file and t 209 function takes a pointer to the DRM file and the GEM object and returns a
207 locally unique handle. When the handle is no 210 locally unique handle. When the handle is no longer needed drivers delete it
208 with a call to drm_gem_handle_delete(). Finall 211 with a call to drm_gem_handle_delete(). Finally the GEM object associated with a
209 handle can be retrieved by a call to drm_gem_o 212 handle can be retrieved by a call to drm_gem_object_lookup().
210 213
211 Handles don't take ownership of GEM objects, t 214 Handles don't take ownership of GEM objects, they only take a reference
212 to the object that will be dropped when the ha 215 to the object that will be dropped when the handle is destroyed. To
213 avoid leaking GEM objects, drivers must make s 216 avoid leaking GEM objects, drivers must make sure they drop the
214 reference(s) they own (such as the initial ref 217 reference(s) they own (such as the initial reference taken at object
215 creation time) as appropriate, without any spe 218 creation time) as appropriate, without any special consideration for the
216 handle. For example, in the particular case of 219 handle. For example, in the particular case of combined GEM object and
217 handle creation in the implementation of the d 220 handle creation in the implementation of the dumb_create operation,
218 drivers must drop the initial reference to the 221 drivers must drop the initial reference to the GEM object before
219 returning the handle. 222 returning the handle.
220 223
221 GEM names are similar in purpose to handles bu 224 GEM names are similar in purpose to handles but are not local to DRM
222 files. They can be passed between processes to 225 files. They can be passed between processes to reference a GEM object
223 globally. Names can't be used directly to refe 226 globally. Names can't be used directly to refer to objects in the DRM
224 API, applications must convert handles to name 227 API, applications must convert handles to names and names to handles
225 using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GE 228 using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
226 respectively. The conversion is handled by the 229 respectively. The conversion is handled by the DRM core without any
227 driver-specific support. 230 driver-specific support.
228 231
229 GEM also supports buffer sharing with dma-buf 232 GEM also supports buffer sharing with dma-buf file descriptors through
230 PRIME. GEM-based drivers must use the provided 233 PRIME. GEM-based drivers must use the provided helpers functions to
231 implement the exporting and importing correctl 234 implement the exporting and importing correctly. See ?. Since sharing
232 file descriptors is inherently more secure tha 235 file descriptors is inherently more secure than the easily guessable and
233 global GEM names it is the preferred buffer sh 236 global GEM names it is the preferred buffer sharing mechanism. Sharing
234 buffers through GEM names is only supported fo 237 buffers through GEM names is only supported for legacy userspace.
235 Furthermore PRIME also allows cross-device buf 238 Furthermore PRIME also allows cross-device buffer sharing since it is
236 based on dma-bufs. 239 based on dma-bufs.
237 240
238 GEM Objects Mapping 241 GEM Objects Mapping
239 ------------------- 242 -------------------
240 243
241 Because mapping operations are fairly heavywei 244 Because mapping operations are fairly heavyweight GEM favours
242 read/write-like access to buffers, implemented 245 read/write-like access to buffers, implemented through driver-specific
243 ioctls, over mapping buffers to userspace. How 246 ioctls, over mapping buffers to userspace. However, when random access
244 to the buffer is needed (to perform software r 247 to the buffer is needed (to perform software rendering for instance),
245 direct access to the object can be more effici 248 direct access to the object can be more efficient.
246 249
247 The mmap system call can't be used directly to 250 The mmap system call can't be used directly to map GEM objects, as they
248 don't have their own file handle. Two alternat 251 don't have their own file handle. Two alternative methods currently
249 co-exist to map GEM objects to userspace. The 252 co-exist to map GEM objects to userspace. The first method uses a
250 driver-specific ioctl to perform the mapping o 253 driver-specific ioctl to perform the mapping operation, calling
251 do_mmap() under the hood. This is often consid 254 do_mmap() under the hood. This is often considered
252 dubious, seems to be discouraged for new GEM-e 255 dubious, seems to be discouraged for new GEM-enabled drivers, and will
253 thus not be described here. 256 thus not be described here.
254 257
255 The second method uses the mmap system call on 258 The second method uses the mmap system call on the DRM file handle. void
256 \*mmap(void \*addr, size_t length, int prot, i 259 \*mmap(void \*addr, size_t length, int prot, int flags, int fd, off_t
257 offset); DRM identifies the GEM object to be m 260 offset); DRM identifies the GEM object to be mapped by a fake offset
258 passed through the mmap offset argument. Prior 261 passed through the mmap offset argument. Prior to being mapped, a GEM
259 object must thus be associated with a fake off 262 object must thus be associated with a fake offset. To do so, drivers
260 must call drm_gem_create_mmap_offset() on the 263 must call drm_gem_create_mmap_offset() on the object.
261 264
262 Once allocated, the fake offset value must be 265 Once allocated, the fake offset value must be passed to the application
263 in a driver-specific way and can then be used 266 in a driver-specific way and can then be used as the mmap offset
264 argument. 267 argument.
265 268
266 The GEM core provides a helper method drm_gem_ 269 The GEM core provides a helper method drm_gem_mmap() to
267 handle object mapping. The method can be set d 270 handle object mapping. The method can be set directly as the mmap file
268 operation handler. It will look up the GEM obj 271 operation handler. It will look up the GEM object based on the offset
269 value and set the VMA operations to the :c:typ 272 value and set the VMA operations to the :c:type:`struct drm_driver
270 <drm_driver>` gem_vm_ops field. Note that drm_ 273 <drm_driver>` gem_vm_ops field. Note that drm_gem_mmap() doesn't map memory to
271 userspace, but relies on the driver-provided f 274 userspace, but relies on the driver-provided fault handler to map pages
272 individually. 275 individually.
273 276
274 To use drm_gem_mmap(), drivers must fill the s 277 To use drm_gem_mmap(), drivers must fill the struct :c:type:`struct drm_driver
275 <drm_driver>` gem_vm_ops field with a pointer 278 <drm_driver>` gem_vm_ops field with a pointer to VM operations.
276 279
277 The VM operations is a :c:type:`struct vm_oper 280 The VM operations is a :c:type:`struct vm_operations_struct <vm_operations_struct>`
278 made up of several fields, the more interestin 281 made up of several fields, the more interesting ones being:
279 282
280 .. code-block:: c 283 .. code-block:: c
281 284
282 struct vm_operations_struct { 285 struct vm_operations_struct {
283 void (*open)(struct vm_area_st 286 void (*open)(struct vm_area_struct * area);
284 void (*close)(struct vm_area_s 287 void (*close)(struct vm_area_struct * area);
285 vm_fault_t (*fault)(struct vm_ 288 vm_fault_t (*fault)(struct vm_fault *vmf);
286 }; 289 };
287 290
288 291
289 The open and close operations must update the 292 The open and close operations must update the GEM object reference
290 count. Drivers can use the drm_gem_vm_open() a 293 count. Drivers can use the drm_gem_vm_open() and drm_gem_vm_close() helper
291 functions directly as open and close handlers. 294 functions directly as open and close handlers.
292 295
293 The fault operation handler is responsible for 296 The fault operation handler is responsible for mapping individual pages
294 to userspace when a page fault occurs. Dependi 297 to userspace when a page fault occurs. Depending on the memory
295 allocation scheme, drivers can allocate pages 298 allocation scheme, drivers can allocate pages at fault time, or can
296 decide to allocate memory for the GEM object a 299 decide to allocate memory for the GEM object at the time the object is
297 created. 300 created.
298 301
299 Drivers that want to map the GEM object upfron 302 Drivers that want to map the GEM object upfront instead of handling page
300 faults can implement their own mmap file opera 303 faults can implement their own mmap file operation handler.
301 304
302 For platforms without MMU the GEM core provide 305 For platforms without MMU the GEM core provides a helper method
303 drm_gem_dma_get_unmapped_area(). The mmap() ro !! 306 drm_gem_cma_get_unmapped_area(). The mmap() routines will call this to get a
304 proposed address for the mapping. 307 proposed address for the mapping.
305 308
306 To use drm_gem_dma_get_unmapped_area(), driver !! 309 To use drm_gem_cma_get_unmapped_area(), drivers must fill the struct
307 :c:type:`struct file_operations <file_operatio 310 :c:type:`struct file_operations <file_operations>` get_unmapped_area field with
308 a pointer on drm_gem_dma_get_unmapped_area(). !! 311 a pointer on drm_gem_cma_get_unmapped_area().
309 312
310 More detailed information about get_unmapped_a 313 More detailed information about get_unmapped_area can be found in
311 Documentation/admin-guide/mm/nommu-mmap.rst 314 Documentation/admin-guide/mm/nommu-mmap.rst
312 315
313 Memory Coherency 316 Memory Coherency
314 ---------------- 317 ----------------
315 318
316 When mapped to the device or used in a command 319 When mapped to the device or used in a command buffer, backing pages for
317 an object are flushed to memory and marked wri 320 an object are flushed to memory and marked write combined so as to be
318 coherent with the GPU. Likewise, if the CPU ac 321 coherent with the GPU. Likewise, if the CPU accesses an object after the
319 GPU has finished rendering to the object, then 322 GPU has finished rendering to the object, then the object must be made
320 coherent with the CPU's view of memory, usuall 323 coherent with the CPU's view of memory, usually involving GPU cache
321 flushing of various kinds. This core CPU<->GPU 324 flushing of various kinds. This core CPU<->GPU coherency management is
322 provided by a device-specific ioctl, which eva 325 provided by a device-specific ioctl, which evaluates an object's current
323 domain and performs any necessary flushing or 326 domain and performs any necessary flushing or synchronization to put the
324 object into the desired coherency domain (note 327 object into the desired coherency domain (note that the object may be
325 busy, i.e. an active render target; in that ca 328 busy, i.e. an active render target; in that case, setting the domain
326 blocks the client and waits for rendering to c 329 blocks the client and waits for rendering to complete before performing
327 any necessary flushing operations). 330 any necessary flushing operations).
328 331
329 Command Execution 332 Command Execution
330 ----------------- 333 -----------------
331 334
332 Perhaps the most important GEM function for GP 335 Perhaps the most important GEM function for GPU devices is providing a
333 command execution interface to clients. Client 336 command execution interface to clients. Client programs construct
334 command buffers containing references to previ 337 command buffers containing references to previously allocated memory
335 objects, and then submit them to GEM. At that 338 objects, and then submit them to GEM. At that point, GEM takes care to
336 bind all the objects into the GTT, execute the 339 bind all the objects into the GTT, execute the buffer, and provide
337 necessary synchronization between clients acce 340 necessary synchronization between clients accessing the same buffers.
338 This often involves evicting some objects from 341 This often involves evicting some objects from the GTT and re-binding
339 others (a fairly expensive operation), and pro 342 others (a fairly expensive operation), and providing relocation support
340 which hides fixed GTT offsets from clients. Cl 343 which hides fixed GTT offsets from clients. Clients must take care not
341 to submit command buffers that reference more 344 to submit command buffers that reference more objects than can fit in
342 the GTT; otherwise, GEM will reject them and n 345 the GTT; otherwise, GEM will reject them and no rendering will occur.
343 Similarly, if several objects in the buffer re 346 Similarly, if several objects in the buffer require fence registers to
344 be allocated for correct rendering (e.g. 2D bl 347 be allocated for correct rendering (e.g. 2D blits on pre-965 chips),
345 care must be taken not to require more fence r 348 care must be taken not to require more fence registers than are
346 available to the client. Such resource managem 349 available to the client. Such resource management should be abstracted
347 from the client in libdrm. 350 from the client in libdrm.
348 351
349 GEM Function Reference 352 GEM Function Reference
350 ---------------------- 353 ----------------------
351 354
352 .. kernel-doc:: include/drm/drm_gem.h 355 .. kernel-doc:: include/drm/drm_gem.h
353 :internal: 356 :internal:
354 357
355 .. kernel-doc:: drivers/gpu/drm/drm_gem.c 358 .. kernel-doc:: drivers/gpu/drm/drm_gem.c
356 :export: 359 :export:
357 360
358 GEM DMA Helper Functions Reference !! 361 GEM CMA Helper Functions Reference
359 ---------------------------------- 362 ----------------------------------
360 363
361 .. kernel-doc:: drivers/gpu/drm/drm_gem_dma_he !! 364 .. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c
362 :doc: dma helpers !! 365 :doc: cma helpers
363 366
364 .. kernel-doc:: include/drm/drm_gem_dma_helper !! 367 .. kernel-doc:: include/drm/drm_gem_cma_helper.h
365 :internal: 368 :internal:
366 369
367 .. kernel-doc:: drivers/gpu/drm/drm_gem_dma_he !! 370 .. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c
368 :export: 371 :export:
369 372
370 GEM SHMEM Helper Function Reference 373 GEM SHMEM Helper Function Reference
371 ----------------------------------- 374 -----------------------------------
372 375
373 .. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_ 376 .. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_helper.c
374 :doc: overview 377 :doc: overview
375 378
376 .. kernel-doc:: include/drm/drm_gem_shmem_help 379 .. kernel-doc:: include/drm/drm_gem_shmem_helper.h
377 :internal: 380 :internal:
378 381
379 .. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_ 382 .. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_helper.c
380 :export: 383 :export:
381 384
382 GEM VRAM Helper Functions Reference 385 GEM VRAM Helper Functions Reference
383 ----------------------------------- 386 -----------------------------------
384 387
385 .. kernel-doc:: drivers/gpu/drm/drm_gem_vram_h 388 .. kernel-doc:: drivers/gpu/drm/drm_gem_vram_helper.c
386 :doc: overview 389 :doc: overview
387 390
388 .. kernel-doc:: include/drm/drm_gem_vram_helpe 391 .. kernel-doc:: include/drm/drm_gem_vram_helper.h
389 :internal: 392 :internal:
390 393
391 .. kernel-doc:: drivers/gpu/drm/drm_gem_vram_h 394 .. kernel-doc:: drivers/gpu/drm/drm_gem_vram_helper.c
392 :export: 395 :export:
393 396
394 GEM TTM Helper Functions Reference 397 GEM TTM Helper Functions Reference
395 ----------------------------------- 398 -----------------------------------
396 399
397 .. kernel-doc:: drivers/gpu/drm/drm_gem_ttm_he 400 .. kernel-doc:: drivers/gpu/drm/drm_gem_ttm_helper.c
398 :doc: overview 401 :doc: overview
399 402
400 .. kernel-doc:: drivers/gpu/drm/drm_gem_ttm_he 403 .. kernel-doc:: drivers/gpu/drm/drm_gem_ttm_helper.c
401 :export: 404 :export:
402 405
403 VMA Offset Manager 406 VMA Offset Manager
404 ================== 407 ==================
405 408
406 .. kernel-doc:: drivers/gpu/drm/drm_vma_manage 409 .. kernel-doc:: drivers/gpu/drm/drm_vma_manager.c
407 :doc: vma offset manager 410 :doc: vma offset manager
408 411
409 .. kernel-doc:: include/drm/drm_vma_manager.h 412 .. kernel-doc:: include/drm/drm_vma_manager.h
410 :internal: 413 :internal:
411 414
412 .. kernel-doc:: drivers/gpu/drm/drm_vma_manage 415 .. kernel-doc:: drivers/gpu/drm/drm_vma_manager.c
413 :export: 416 :export:
414 417
415 .. _prime_buffer_sharing: 418 .. _prime_buffer_sharing:
416 419
417 PRIME Buffer Sharing 420 PRIME Buffer Sharing
418 ==================== 421 ====================
419 422
420 PRIME is the cross device buffer sharing frame 423 PRIME is the cross device buffer sharing framework in drm, originally
421 created for the OPTIMUS range of multi-gpu pla 424 created for the OPTIMUS range of multi-gpu platforms. To userspace PRIME
422 buffers are dma-buf based file descriptors. 425 buffers are dma-buf based file descriptors.
423 426
424 Overview and Lifetime Rules 427 Overview and Lifetime Rules
425 --------------------------- 428 ---------------------------
426 429
427 .. kernel-doc:: drivers/gpu/drm/drm_prime.c 430 .. kernel-doc:: drivers/gpu/drm/drm_prime.c
428 :doc: overview and lifetime rules 431 :doc: overview and lifetime rules
429 432
430 PRIME Helper Functions 433 PRIME Helper Functions
431 ---------------------- 434 ----------------------
432 435
433 .. kernel-doc:: drivers/gpu/drm/drm_prime.c 436 .. kernel-doc:: drivers/gpu/drm/drm_prime.c
434 :doc: PRIME Helpers 437 :doc: PRIME Helpers
435 438
436 PRIME Function References 439 PRIME Function References
437 ------------------------- 440 -------------------------
438 441
439 .. kernel-doc:: include/drm/drm_prime.h 442 .. kernel-doc:: include/drm/drm_prime.h
440 :internal: 443 :internal:
441 444
442 .. kernel-doc:: drivers/gpu/drm/drm_prime.c 445 .. kernel-doc:: drivers/gpu/drm/drm_prime.c
443 :export: 446 :export:
444 447
445 DRM MM Range Allocator 448 DRM MM Range Allocator
446 ====================== 449 ======================
447 450
448 Overview 451 Overview
449 -------- 452 --------
450 453
451 .. kernel-doc:: drivers/gpu/drm/drm_mm.c 454 .. kernel-doc:: drivers/gpu/drm/drm_mm.c
452 :doc: Overview 455 :doc: Overview
453 456
454 LRU Scan/Eviction Support 457 LRU Scan/Eviction Support
455 ------------------------- 458 -------------------------
456 459
457 .. kernel-doc:: drivers/gpu/drm/drm_mm.c 460 .. kernel-doc:: drivers/gpu/drm/drm_mm.c
458 :doc: lru scan roster 461 :doc: lru scan roster
459 462
460 DRM MM Range Allocator Function References 463 DRM MM Range Allocator Function References
461 ------------------------------------------ 464 ------------------------------------------
462 465
463 .. kernel-doc:: include/drm/drm_mm.h 466 .. kernel-doc:: include/drm/drm_mm.h
464 :internal: 467 :internal:
465 468
466 .. kernel-doc:: drivers/gpu/drm/drm_mm.c 469 .. kernel-doc:: drivers/gpu/drm/drm_mm.c
467 :export: 470 :export:
468 471
469 .. _drm_gpuvm: <<
470 <<
471 DRM GPUVM <<
472 ========= <<
473 <<
474 Overview <<
475 -------- <<
476 <<
477 .. kernel-doc:: drivers/gpu/drm/drm_gpuvm.c <<
478 :doc: Overview <<
479 <<
480 Split and Merge <<
481 --------------- <<
482 <<
483 .. kernel-doc:: drivers/gpu/drm/drm_gpuvm.c <<
484 :doc: Split and Merge <<
485 <<
486 .. _drm_gpuvm_locking: <<
487 <<
488 Locking <<
489 ------- <<
490 <<
491 .. kernel-doc:: drivers/gpu/drm/drm_gpuvm.c <<
492 :doc: Locking <<
493 <<
494 Examples <<
495 -------- <<
496 <<
497 .. kernel-doc:: drivers/gpu/drm/drm_gpuvm.c <<
498 :doc: Examples <<
499 <<
500 DRM GPUVM Function References <<
501 ----------------------------- <<
502 <<
503 .. kernel-doc:: include/drm/drm_gpuvm.h <<
504 :internal: <<
505 <<
506 .. kernel-doc:: drivers/gpu/drm/drm_gpuvm.c <<
507 :export: <<
508 <<
509 DRM Buddy Allocator <<
510 =================== <<
511 <<
512 DRM Buddy Function References <<
513 ----------------------------- <<
514 <<
515 .. kernel-doc:: drivers/gpu/drm/drm_buddy.c <<
516 :export: <<
517 <<
518 DRM Cache Handling and Fast WC memcpy() 472 DRM Cache Handling and Fast WC memcpy()
519 ======================================= 473 =======================================
520 474
521 .. kernel-doc:: drivers/gpu/drm/drm_cache.c 475 .. kernel-doc:: drivers/gpu/drm/drm_cache.c
522 :export: 476 :export:
523 477
524 .. _drm_sync_objects: <<
525 <<
526 DRM Sync Objects 478 DRM Sync Objects
527 ================ !! 479 ===========================
528 480
529 .. kernel-doc:: drivers/gpu/drm/drm_syncobj.c 481 .. kernel-doc:: drivers/gpu/drm/drm_syncobj.c
530 :doc: Overview 482 :doc: Overview
531 483
532 .. kernel-doc:: include/drm/drm_syncobj.h 484 .. kernel-doc:: include/drm/drm_syncobj.h
533 :internal: 485 :internal:
534 486
535 .. kernel-doc:: drivers/gpu/drm/drm_syncobj.c 487 .. kernel-doc:: drivers/gpu/drm/drm_syncobj.c
536 :export: 488 :export:
537 489
538 DRM Execution context <<
539 ===================== <<
540 <<
541 .. kernel-doc:: drivers/gpu/drm/drm_exec.c <<
542 :doc: Overview <<
543 <<
544 .. kernel-doc:: include/drm/drm_exec.h <<
545 :internal: <<
546 <<
547 .. kernel-doc:: drivers/gpu/drm/drm_exec.c <<
548 :export: <<
549 <<
550 GPU Scheduler 490 GPU Scheduler
551 ============= 491 =============
552 492
553 Overview 493 Overview
554 -------- 494 --------
555 495
556 .. kernel-doc:: drivers/gpu/drm/scheduler/sche 496 .. kernel-doc:: drivers/gpu/drm/scheduler/sched_main.c
557 :doc: Overview 497 :doc: Overview
558 498
559 Flow Control <<
560 ------------ <<
561 <<
562 .. kernel-doc:: drivers/gpu/drm/scheduler/sche <<
563 :doc: Flow Control <<
564 <<
565 Scheduler Function References 499 Scheduler Function References
566 ----------------------------- 500 -----------------------------
567 501
568 .. kernel-doc:: include/drm/gpu_scheduler.h 502 .. kernel-doc:: include/drm/gpu_scheduler.h
569 :internal: 503 :internal:
570 504
571 .. kernel-doc:: drivers/gpu/drm/scheduler/sche 505 .. kernel-doc:: drivers/gpu/drm/scheduler/sched_main.c
572 :export: <<
573 <<
574 .. kernel-doc:: drivers/gpu/drm/scheduler/sche <<
575 :export: 506 :export:
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