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