1.. SPDX-License-Identifier: GPL-2.0
2
3=====
4spufs
5=====
6
7Name
8====
9
10       spufs - the SPU file system
11
12
13Description
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
30Mount 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
40Files
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
260Examples
261========
262       /etc/fstab entry
263              none      /spu      spufs     gid=spu   0    0
264
265
266Authors
267=======
268       Arnd  Bergmann  <arndb@de.ibm.com>,  Mark  Nutter <mnutter@us.ibm.com>,
269       Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
270
271See Also
272========
273       capabilities(7), close(2), spu_create(2), spu_run(2), spufs(7)
274