1 ========================== 1 ==========================
2 I915 Small BAR RFC Section 2 I915 Small BAR RFC Section
3 ========================== 3 ==========================
4 Starting from DG2 we will have resizable BAR s 4 Starting from DG2 we will have resizable BAR support for device local-memory(i.e
5 I915_MEMORY_CLASS_DEVICE), but in some cases t 5 I915_MEMORY_CLASS_DEVICE), but in some cases the final BAR size might still be
6 smaller than the total probed_size. In such ca 6 smaller than the total probed_size. In such cases, only some subset of
7 I915_MEMORY_CLASS_DEVICE will be CPU accessibl 7 I915_MEMORY_CLASS_DEVICE will be CPU accessible(for example the first 256M),
8 while the remainder is only accessible via the 8 while the remainder is only accessible via the GPU.
9 9
10 I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS flag 10 I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS flag
11 ---------------------------------------------- 11 ----------------------------------------------
12 New gem_create_ext flag to tell the kernel tha 12 New gem_create_ext flag to tell the kernel that a BO will require CPU access.
13 This becomes important when placing an object 13 This becomes important when placing an object in I915_MEMORY_CLASS_DEVICE, where
14 underneath the device has a small BAR, meaning 14 underneath the device has a small BAR, meaning only some portion of it is CPU
15 accessible. Without this flag the kernel will 15 accessible. Without this flag the kernel will assume that CPU access is not
16 required, and prioritize using the non-CPU vis 16 required, and prioritize using the non-CPU visible portion of
17 I915_MEMORY_CLASS_DEVICE. 17 I915_MEMORY_CLASS_DEVICE.
18 18
19 .. kernel-doc:: Documentation/gpu/rfc/i915_sma 19 .. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h
20 :functions: __drm_i915_gem_create_ext 20 :functions: __drm_i915_gem_create_ext
21 21
22 probed_cpu_visible_size attribute 22 probed_cpu_visible_size attribute
23 --------------------------------- 23 ---------------------------------
24 New struct__drm_i915_memory_region attribute w 24 New struct__drm_i915_memory_region attribute which returns the total size of the
25 CPU accessible portion, for the particular reg 25 CPU accessible portion, for the particular region. This should only be
26 applicable for I915_MEMORY_CLASS_DEVICE. We al 26 applicable for I915_MEMORY_CLASS_DEVICE. We also report the
27 unallocated_cpu_visible_size, alongside the un 27 unallocated_cpu_visible_size, alongside the unallocated_size.
28 28
29 Vulkan will need this as part of creating a se 29 Vulkan will need this as part of creating a separate VkMemoryHeap with the
30 VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT set, to re 30 VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT set, to represent the CPU visible portion,
31 where the total size of the heap needs to be k 31 where the total size of the heap needs to be known. It also wants to be able to
32 give a rough estimate of how memory can potent 32 give a rough estimate of how memory can potentially be allocated.
33 33
34 .. kernel-doc:: Documentation/gpu/rfc/i915_sma 34 .. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h
35 :functions: __drm_i915_memory_region_info 35 :functions: __drm_i915_memory_region_info
36 36
37 Error Capture restrictions 37 Error Capture restrictions
38 -------------------------- 38 --------------------------
39 With error capture we have two new restriction 39 With error capture we have two new restrictions:
40 40
41 1) Error capture is best effort on small B 41 1) Error capture is best effort on small BAR systems; if the pages are not
42 CPU accessible, at the time of capture, th 42 CPU accessible, at the time of capture, then the kernel is free to skip
43 trying to capture them. 43 trying to capture them.
44 44
45 2) On discrete and newer integrated platfo 45 2) On discrete and newer integrated platforms we now reject error capture
46 on recoverable contexts. In the future the 46 on recoverable contexts. In the future the kernel may want to blit during
47 error capture, when for example something 47 error capture, when for example something is not currently CPU accessible.
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