1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 ===== 3 =====
4 spufs 4 spufs
5 ===== 5 =====
6 6
7 Name 7 Name
8 ==== 8 ====
9 9
10 spufs - the SPU file system 10 spufs - the SPU file system
11 11
12 12
13 Description 13 Description
14 =========== 14 ===========
15 15
16 The SPU file system is used on PowerPC 16 The SPU file system is used on PowerPC machines that implement the Cell
17 Broadband Engine Architecture in order 17 Broadband Engine Architecture in order to access Synergistic Processor
18 Units (SPUs). 18 Units (SPUs).
19 19
20 The file system provides a name space s 20 The file system provides a name space similar to posix shared memory or
21 message queues. Users that have write p 21 message queues. Users that have write permissions on the file system
22 can use spu_create(2) to establish SPU 22 can use spu_create(2) to establish SPU contexts in the spufs root.
23 23
24 Every SPU context is represented by a d 24 Every SPU context is represented by a directory containing a predefined
25 set of files. These files can be used f 25 set of files. These files can be used for manipulating the state of the
26 logical SPU. Users can change permissio 26 logical SPU. Users can change permissions on those files, but not actu-
27 ally add or remove files. 27 ally add or remove files.
28 28
29 29
30 Mount Options 30 Mount Options
31 ============= 31 =============
32 32
33 uid=<uid> 33 uid=<uid>
34 set the user owning the mount po 34 set the user owning the mount point, the default is 0 (root).
35 35
36 gid=<gid> 36 gid=<gid>
37 set the group owning the mount p 37 set the group owning the mount point, the default is 0 (root).
38 38
39 39
40 Files 40 Files
41 ===== 41 =====
42 42
43 The files in spufs mostly follow the st 43 The files in spufs mostly follow the standard behavior for regular sys-
44 tem calls like read(2) or write(2), bu 44 tem calls like read(2) or write(2), but often support only a subset of
45 the operations supported on regular fil 45 the operations supported on regular file systems. This list details the
46 supported operations and the deviat 46 supported operations and the deviations from the behaviour in the
47 respective man pages. 47 respective man pages.
48 48
49 All files that support the read(2) oper 49 All files that support the read(2) operation also support readv(2) and
50 all files that support the write(2) o 50 all files that support the write(2) operation also support writev(2).
51 All files support the access(2) and sta 51 All files support the access(2) and stat(2) family of operations, but
52 only the st_mode, st_nlink, st_uid 52 only the st_mode, st_nlink, st_uid and st_gid fields of struct stat
53 contain reliable information. 53 contain reliable information.
54 54
55 All files support the chmod(2)/fchmod(2 55 All files support the chmod(2)/fchmod(2) and chown(2)/fchown(2) opera-
56 tions, but will not be able to grant 56 tions, but will not be able to grant permissions that contradict the
57 possible operations, e.g. read access o 57 possible operations, e.g. read access on the wbox file.
58 58
59 The current set of files is: 59 The current set of files is:
60 60
61 61
62 /mem 62 /mem
63 the contents of the local storage memor 63 the contents of the local storage memory of the SPU. This can be
64 accessed like a regular shared memory 64 accessed like a regular shared memory file and contains both code and
65 data in the address space of the SPU. 65 data in the address space of the SPU. The possible operations on an
66 open mem file are: 66 open mem file are:
67 67
68 read(2), pread(2), write(2), pwrite(2), 68 read(2), pread(2), write(2), pwrite(2), lseek(2)
69 These operate as documented, 69 These operate as documented, with the exception that seek(2),
70 write(2) and pwrite(2) are not s 70 write(2) and pwrite(2) are not supported beyond the end of the
71 file. The file size is the size 71 file. The file size is the size of the local storage of the SPU,
72 which normally is 256 kilobytes. 72 which normally is 256 kilobytes.
73 73
74 mmap(2) 74 mmap(2)
75 Mapping mem into the process add 75 Mapping mem into the process address space gives access to the
76 SPU local storage within the 76 SPU local storage within the process address space. Only
77 MAP_SHARED mappings are allowed. 77 MAP_SHARED mappings are allowed.
78 78
79 79
80 /mbox 80 /mbox
81 The first SPU to CPU communication mail 81 The first SPU to CPU communication mailbox. This file is read-only and
82 can be read in units of 32 bits. T 82 can be read in units of 32 bits. The file can only be used in non-
83 blocking mode and it even poll() will n 83 blocking mode and it even poll() will not block on it. The possible
84 operations on an open mbox file are: 84 operations on an open mbox file are:
85 85
86 read(2) 86 read(2)
87 If a count smaller than four i 87 If a count smaller than four is requested, read returns -1 and
88 sets errno to EINVAL. If there 88 sets errno to EINVAL. If there is no data available in the mail
89 box, the return value is set 89 box, the return value is set to -1 and errno becomes EAGAIN.
90 When data has been read successf 90 When data has been read successfully, four bytes are placed in
91 the data buffer and the value fo 91 the data buffer and the value four is returned.
92 92
93 93
94 /ibox 94 /ibox
95 The second SPU to CPU communication 95 The second SPU to CPU communication mailbox. This file is similar to
96 the first mailbox file, but can be read 96 the first mailbox file, but can be read in blocking I/O mode, and the
97 poll family of system calls can be use 97 poll family of system calls can be used to wait for it. The possible
98 operations on an open ibox file are: 98 operations on an open ibox file are:
99 99
100 read(2) 100 read(2)
101 If a count smaller than four is 101 If a count smaller than four is requested, read returns -1 and
102 sets errno to EINVAL. If there 102 sets errno to EINVAL. If there is no data available in the mail
103 box and the file descriptor has 103 box and the file descriptor has been opened with O_NONBLOCK, the
104 return value is set to -1 and er 104 return value is set to -1 and errno becomes EAGAIN.
105 105
106 If there is no data availab 106 If there is no data available in the mail box and the file
107 descriptor has been opened witho 107 descriptor has been opened without O_NONBLOCK, the call will
108 block until the SPU writes t 108 block until the SPU writes to its interrupt mailbox channel.
109 When data has been read successf 109 When data has been read successfully, four bytes are placed in
110 the data buffer and the value fo 110 the data buffer and the value four is returned.
111 111
112 poll(2) 112 poll(2)
113 Poll on the ibox file return 113 Poll on the ibox file returns (POLLIN | POLLRDNORM) whenever
114 data is available for reading. 114 data is available for reading.
115 115
116 116
117 /wbox 117 /wbox
118 The CPU to SPU communation mailbox. It 118 The CPU to SPU communation mailbox. It is write-only and can be written
119 in units of 32 bits. If the mailbox 119 in units of 32 bits. If the mailbox is full, write() will block and
120 poll can be used to wait for it becomin 120 poll can be used to wait for it becoming empty again. The possible
121 operations on an open wbox file are: 121 operations on an open wbox file are: write(2) If a count smaller than
122 four is requested, write returns -1 and 122 four is requested, write returns -1 and sets errno to EINVAL. If there
123 is no space available in the mail box 123 is no space available in the mail box and the file descriptor has been
124 opened with O_NONBLOCK, the return valu 124 opened with O_NONBLOCK, the return value is set to -1 and errno becomes
125 EAGAIN. 125 EAGAIN.
126 126
127 If there is no space available in the 127 If there is no space available in the mail box and the file descriptor
128 has been opened without O_NONBLOCK, the 128 has been opened without O_NONBLOCK, the call will block until the SPU
129 reads from its PPE mailbox channel. 129 reads from its PPE mailbox channel. When data has been read success-
130 fully, four bytes are placed in the dat 130 fully, four bytes are placed in the data buffer and the value four is
131 returned. 131 returned.
132 132
133 poll(2) 133 poll(2)
134 Poll on the ibox file returns 134 Poll on the ibox file returns (POLLOUT | POLLWRNORM) whenever
135 space is available for writing. 135 space is available for writing.
136 136
137 137
138 /mbox_stat, /ibox_stat, /wbox_stat 138 /mbox_stat, /ibox_stat, /wbox_stat
139 Read-only files that contain the length 139 Read-only files that contain the length of the current queue, i.e. how
140 many words can be read from mbox 140 many words can be read from mbox or ibox or how many words can be
141 written to wbox without blocking. The 141 written to wbox without blocking. The files can be read only in 4-byte
142 units and return a big-endian bina 142 units and return a big-endian binary integer number. The possible
143 operations on an open ``*box_stat`` fil 143 operations on an open ``*box_stat`` file are:
144 144
145 read(2) 145 read(2)
146 If a count smaller than four is 146 If a count smaller than four is requested, read returns -1 and
147 sets errno to EINVAL. Otherwise 147 sets errno to EINVAL. Otherwise, a four byte value is placed in
148 the data buffer, containing the 148 the data buffer, containing the number of elements that can be
149 read from (for mbox_stat and 149 read from (for mbox_stat and ibox_stat) or written to (for
150 wbox_stat) the respective mail b 150 wbox_stat) the respective mail box without blocking or resulting
151 in EAGAIN. 151 in EAGAIN.
152 152
153 153
154 /npc, /decr, /decr_status, /spu_tag_mask, / 154 /npc, /decr, /decr_status, /spu_tag_mask, /event_mask, /srr0
155 Internal registers of the SPU. The r 155 Internal registers of the SPU. The representation is an ASCII string
156 with the numeric value of the next inst 156 with the numeric value of the next instruction to be executed. These
157 can be used in read/write mode for de 157 can be used in read/write mode for debugging, but normal operation of
158 programs should not rely on them becaus 158 programs should not rely on them because access to any of them except
159 npc requires an SPU context save and is 159 npc requires an SPU context save and is therefore very inefficient.
160 160
161 The contents of these files are: 161 The contents of these files are:
162 162
163 =================== =================== 163 =================== ===================================
164 npc Next Program Counte 164 npc Next Program Counter
165 decr SPU Decrementer 165 decr SPU Decrementer
166 decr_status Decrementer Status 166 decr_status Decrementer Status
167 spu_tag_mask MFC tag mask for SP 167 spu_tag_mask MFC tag mask for SPU DMA
168 event_mask Event mask for SPU 168 event_mask Event mask for SPU interrupts
169 srr0 Interrupt Return ad 169 srr0 Interrupt Return address register
170 =================== =================== 170 =================== ===================================
171 171
172 172
173 The possible operations on an 173 The possible operations on an open npc, decr, decr_status,
174 spu_tag_mask, event_mask or srr0 file a 174 spu_tag_mask, event_mask or srr0 file are:
175 175
176 read(2) 176 read(2)
177 When the count supplied to the r 177 When the count supplied to the read call is shorter than the
178 required length for the pointer 178 required length for the pointer value plus a newline character,
179 subsequent reads from the same f 179 subsequent reads from the same file descriptor will result in
180 completing the string, regardle 180 completing the string, regardless of changes to the register by
181 a running SPU task. When a comp 181 a running SPU task. When a complete string has been read, all
182 subsequent read operations will 182 subsequent read operations will return zero bytes and a new file
183 descriptor needs to be opened to 183 descriptor needs to be opened to read the value again.
184 184
185 write(2) 185 write(2)
186 A write operation on the file re 186 A write operation on the file results in setting the register to
187 the value given in the strin 187 the value given in the string. The string is parsed from the
188 beginning to the first non-numer 188 beginning to the first non-numeric character or the end of the
189 buffer. Subsequent writes to th 189 buffer. Subsequent writes to the same file descriptor overwrite
190 the previous setting. 190 the previous setting.
191 191
192 192
193 /fpcr 193 /fpcr
194 This file gives access to the Floating 194 This file gives access to the Floating Point Status and Control Regis-
195 ter as a four byte long file. The opera 195 ter as a four byte long file. The operations on the fpcr file are:
196 196
197 read(2) 197 read(2)
198 If a count smaller than four i 198 If a count smaller than four is requested, read returns -1 and
199 sets errno to EINVAL. Otherwise 199 sets errno to EINVAL. Otherwise, a four byte value is placed in
200 the data buffer, containing the 200 the data buffer, containing the current value of the fpcr regis-
201 ter. 201 ter.
202 202
203 write(2) 203 write(2)
204 If a count smaller than four is 204 If a count smaller than four is requested, write returns -1 and
205 sets errno to EINVAL. Otherw 205 sets errno to EINVAL. Otherwise, a four byte value is copied
206 from the data buffer, updating t 206 from the data buffer, updating the value of the fpcr register.
207 207
208 208
209 /signal1, /signal2 209 /signal1, /signal2
210 The two signal notification channels of 210 The two signal notification channels of an SPU. These are read-write
211 files that operate on a 32 bit word 211 files that operate on a 32 bit word. Writing to one of these files
212 triggers an interrupt on the SPU. The 212 triggers an interrupt on the SPU. The value written to the signal
213 files can be read from the SPU through 213 files can be read from the SPU through a channel read or from host user
214 space through the file. After the valu 214 space through the file. After the value has been read by the SPU, it
215 is reset to zero. The possible opera 215 is reset to zero. The possible operations on an open signal1 or sig-
216 nal2 file are: 216 nal2 file are:
217 217
218 read(2) 218 read(2)
219 If a count smaller than four is 219 If a count smaller than four is requested, read returns -1 and
220 sets errno to EINVAL. Otherwise 220 sets errno to EINVAL. Otherwise, a four byte value is placed in
221 the data buffer, containing the 221 the data buffer, containing the current value of the specified
222 signal notification register. 222 signal notification register.
223 223
224 write(2) 224 write(2)
225 If a count smaller than four is 225 If a count smaller than four is requested, write returns -1 and
226 sets errno to EINVAL. Otherwise 226 sets errno to EINVAL. Otherwise, a four byte value is copied
227 from the data buffer, updating t 227 from the data buffer, updating the value of the specified signal
228 notification register. The sign 228 notification register. The signal notification register will
229 either be replaced with the inpu 229 either be replaced with the input data or will be updated to the
230 bitwise OR of the old value and 230 bitwise OR of the old value and the input data, depending on the
231 contents of the signal1_type, 231 contents of the signal1_type, or signal2_type respectively,
232 file. 232 file.
233 233
234 234
235 /signal1_type, /signal2_type 235 /signal1_type, /signal2_type
236 These two files change the behavior of 236 These two files change the behavior of the signal1 and signal2 notifi-
237 cation files. The contain a numeric 237 cation files. The contain a numerical ASCII string which is read as
238 either "1" or "0". In mode 0 (overwrit 238 either "1" or "0". In mode 0 (overwrite), the hardware replaces the
239 contents of the signal channel with the 239 contents of the signal channel with the data that is written to it. in
240 mode 1 (logical OR), the hardware accum 240 mode 1 (logical OR), the hardware accumulates the bits that are subse-
241 quently written to it. The possible op 241 quently written to it. The possible operations on an open signal1_type
242 or signal2_type file are: 242 or signal2_type file are:
243 243
244 read(2) 244 read(2)
245 When the count supplied to the r 245 When the count supplied to the read call is shorter than the
246 required length for the digit 246 required length for the digit plus a newline character, subse-
247 quent reads from the same file d 247 quent reads from the same file descriptor will result in com-
248 pleting the string. When a co 248 pleting the string. When a complete string has been read, all
249 subsequent read operations will 249 subsequent read operations will return zero bytes and a new file
250 descriptor needs to be opened to 250 descriptor needs to be opened to read the value again.
251 251
252 write(2) 252 write(2)
253 A write operation on the file re 253 A write operation on the file results in setting the register to
254 the value given in the string. T 254 the value given in the string. The string is parsed from the
255 beginning to the first non-num 255 beginning to the first non-numeric character or the end of the
256 buffer. Subsequent writes to th 256 buffer. Subsequent writes to the same file descriptor overwrite
257 the previous setting. 257 the previous setting.
258 258
259 259
260 Examples 260 Examples
261 ======== 261 ========
262 /etc/fstab entry 262 /etc/fstab entry
263 none /spu spufs gi 263 none /spu spufs gid=spu 0 0
264 264
265 265
266 Authors 266 Authors
267 ======= 267 =======
268 Arnd Bergmann <arndb@de.ibm.com>, Mar 268 Arnd Bergmann <arndb@de.ibm.com>, Mark Nutter <mnutter@us.ibm.com>,
269 Ulrich Weigand <Ulrich.Weigand@de.ibm.co 269 Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
270 270
271 See Also 271 See Also
272 ======== 272 ========
273 capabilities(7), close(2), spu_create(2 273 capabilities(7), close(2), spu_create(2), spu_run(2), spufs(7)
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