spufs(7)



SPUFS(7)                   Linux Programmer's Manual                  SPUFS(7)

NAME
       spufs - SPU filesystem

DESCRIPTION
       The  SPU filesystem is used on PowerPC machines that implement the Cell
       Broadband Engine Architecture in order to access Synergistic  Processor
       Units (SPUs).

       The  filesystem provides a name space similar to POSIX shared memory or
       message queues.  Users that have write permissions  on  the  filesystem
       can  use  spu_create(2)  to establish SPU contexts under the spufs root
       directory.

       Every SPU context is represented by a directory containing a predefined
       set  of  files.   These files can be used for manipulating the state of
       the logical SPU.  Users can change permissions on the files, but  can't
       add or remove files.

   Mount options
       uid=<uid>
              Set the user owning the mount point; the default is 0 (root).

       gid=<gid>
              Set the group owning the mount point; the default is 0 (root).

       mode=<mode>
              Set  the  mode  of the top-level directory in spufs, as an octal
              mode string.  The default is 0775.

   Files
       The files in spufs mostly follow the standard behavior for regular sys-
       tem  calls like read(2) or write(2), but often support only a subset of
       the operations supported on regular filesystems.  This list details the
       supported  operations and the deviations from the standard behavior de-
       scribed in the respective man pages.

       All files that support the read(2) operation also support readv(2)  and
       all  files  that support the write(2) operation also support writev(2).
       All files support the access(2) and stat(2) family of  operations,  but
       for  the  latter  call,  the only fields of the returned stat structure
       that contain reliable information are st_mode,  st_nlink,  st_uid,  and
       st_gid.

       All  files support the chmod(2)/fchmod(2) and chown(2)/fchown(2) opera-
       tions, but will not be able to grant permissions  that  contradict  the
       possible operations (e.g., read access on the wbox file).

       The current set of files is:

       /capabilities
              Contains  a comma-delimited string representing the capabilities
              of this SPU context.  Possible capabilities are:

              sched  This context may be scheduled.

              step   This context can be run in single-step mode,  for  debug-
                     ging.

              New capabilities flags may be added in the future.

       /mem   the  contents  of the local storage memory of the SPU.  This can
              be accessed like a regular shared memory file and contains  both
              code and data in the address space of the SPU.  The possible op-
              erations on an open mem file are:

              read(2), pread(2), write(2), pwrite(2), lseek(2)
                     These operate as usual, with the exception that lseek(2),
                     write(2),  and pwrite(2) are not supported beyond the end
                     of the file.  The file size is  the  size  of  the  local
                     storage of the SPU, which is normally 256 kilobytes.

              mmap(2)
                     Mapping  mem  into the process address space provides ac-
                     cess to the SPU local storage within the process  address
                     space.  Only MAP_SHARED mappings are allowed.

       /regs  Contains the saved general-purpose registers of the SPU context.
              This file contains the 128-bit values  of  each  register,  from
              register  0 to register 127, in order.  This allows the general-
              purpose registers to be inspected for debugging.

              Reading to or writing from this file requires that  the  context
              is scheduled out, so use of this file is not recommended in nor-
              mal program operation.

              The regs file is not present on contexts that have been  created
              with the SPU_CREATE_NOSCHED flag.

       /mbox  The  first SPU-to-CPU communication mailbox.  This file is read-
              only and can be read in units of 4 bytes.  The file can be  used
              only  in nonblocking mode - even poll(2) cannot be used to block
              on this file.  The only possible operation on an open mbox  file
              is:

              read(2)
                     If  count  is  smaller  than four, read(2) returns -1 and
                     sets errno to EINVAL.  If there is no data  available  in
                     the  mailbox  (i.e.,  the SPU has not sent a mailbox mes-
                     sage), the return value is set to -1 and errno is set  to
                     EAGAIN.  When data has been read successfully, four bytes
                     are placed in the data buffer and the value four  is  re-
                     turned.

       /ibox  The second SPU-to-CPU communication mailbox.  This file is simi-
              lar to the first mailbox file, but can be read in  blocking  I/O
              mode, thus calling read(2) on an open ibox file will block until
              the SPU has written data to its interrupt mailbox  channel  (un-
              less  the  file  has  been  opened  with O_NONBLOCK, see below).
              Also, poll(2) and similar system calls can be  used  to  monitor
              for the presence of mailbox data.

              The possible operations on an open ibox file are:

              read(2)
                     If  count  is  smaller  than four, read(2) returns -1 and
                     sets errno to EINVAL.  If there is no data  available  in
                     the  mailbox and the file descriptor has been opened with
                     O_NONBLOCK, the return value is set to -1  and  errno  is
                     set to EAGAIN.

                     If there is no data available in the mailbox and the file
                     descriptor has been opened without O_NONBLOCK,  the  call
                     will  block until the SPU writes to its interrupt mailbox
                     channel.  When data  has  been  read  successfully,  four
                     bytes are placed in the data buffer and the value four is
                     returned.

              poll(2)
                     Poll on the ibox file returns (POLLIN | POLLRDNORM) when-
                     ever data is available for reading.

       /wbox  The  CPU-to-SPU communication mailbox.  It is write-only and can
              be written in units of four bytes.   If  the  mailbox  is  full,
              write(2)  will block, and poll(2) can be used to block until the
              mailbox is available for writing again.  The possible operations
              on an open wbox file are:

              write(2)
                     If  count  is  smaller than four, write(2) returns -1 and
                     sets errno to EINVAL.  If there is no space available  in
                     the  mailbox and the file descriptor has been opened with
                     O_NONBLOCK, the return value is set to -1  and  errno  is
                     set to EAGAIN.

                     If  there  is  no  space available in the mailbox and the
                     file descriptor has been opened without  O_NONBLOCK,  the
                     call will block until the SPU reads from its PPE (PowerPC
                     Processing Element) mailbox channel.  When data has  been
                     written successfully, the system call returns four as its
                     function result.

              poll(2)
                     A poll on the wbox file returns  (POLLOUT  |  POLLWRNORM)
                     whenever space is available for writing.

       /mbox_stat, /ibox_stat, /wbox_stat
              These are read-only files that contain the length of the current
              queue of each mailbox--that is, how many words can be read  from
              mbox  or  ibox  or how many words can be written to wbox without
              blocking.  The files can be read only in four-byte units and re-
              turn  a big-endian binary integer number.  The only possible op-
              eration on an open *box_stat file is:

              read(2)
                     If count is smaller than four,  read(2)  returns  -1  and
                     sets  errno  to  EINVAL.  Otherwise, a four-byte value is
                     placed in the data buffer.  This value is the  number  of
                     elements  that  can  be  read  from  (for  mbox_stat  and
                     ibox_stat) or written to (for wbox_stat)  the  respective
                     mailbox without blocking or returning an EAGAIN error.

       /npc,  /decr,  /decr_status, /spu_tag_mask, /event_mask, /event_status,
       /srr0, /lslr
              Internal registers of the SPU.  These  files  contain  an  ASCII
              string  representing  the  hex  value of the specified register.
              Reads and writes on these files (except for npc, see below)  re-
              quire  that the SPU context be scheduled out, so frequent access
              to these files is not recommended for normal program operation.

              The contents of these files are:

              npc             Next Program Counter - valid only when  the  SPU
                              is in a stopped state.

              decr            SPU Decrementer

              decr_status     Decrementer Status

              spu_tag_mask    MFC tag mask for SPU DMA

              event_mask      Event mask for SPU interrupts

              event_status    Number of SPU events pending (read-only)

              srr0            Interrupt Return address register

              lslr            Local Store Limit Register

              The possible operations on these files are:

              read(2)
                     Reads  the current register value.  If the register value
                     is larger than the buffer passed to  the  read(2)  system
                     call,  subsequent  reads  will  continue reading from the
                     same buffer, until the end of the buffer is reached.

                     When a complete string has been read, all subsequent read
                     operations will return zero bytes and a new file descrip-
                     tor needs to be opened to read a new value.

              write(2)
                     A write(2) operation on the file sets the register to the
                     value given in the string.  The string is parsed from the
                     beginning until the first nonnumeric character or the end
                     of  the  buffer.   Subsequent writes to the same file de-
                     scriptor overwrite the previous setting.

                     Except for the npc file, these files are not  present  on
                     contexts   that  have  been  created  with  the  SPU_CRE-
                     ATE_NOSCHED flag.

       /fpcr  This file provides access to the Floating Point Status and  Con-
              trol  Register  (fcpr)  as a binary, four-byte file.  The opera-
              tions on the fpcr file are:

              read(2)
                     If count is smaller than four,  read(2)  returns  -1  and
                     sets  errno  to  EINVAL.  Otherwise, a four-byte value is
                     placed in the data buffer; this is the current  value  of
                     the fpcr register.

              write(2)
                     If  count  is  smaller than four, write(2) returns -1 and
                     sets errno to EINVAL.  Otherwise, a  four-byte  value  is
                     copied  from  the  data buffer, updating the value of the
                     fpcr register.

       /signal1, /signal2
              The files provide access to the two signal notification channels
              of an SPU.  These are read-write files that operate on four-byte
              words.  Writing to one of these files triggers an  interrupt  on
              the SPU.  The value written to the signal files can be read from
              the SPU through a channel read or from host user  space  through
              the file.  After the value has been read by the SPU, it is reset
              to zero.  The possible operations on an open signal1 or  signal2
              file are:

              read(2)
                     If  count  is  smaller  than four, read(2) returns -1 and
                     sets errno to EINVAL.  Otherwise, a  four-byte  value  is
                     placed  in  the data buffer; this is the current value of
                     the specified signal notification register.

              write(2)
                     If count is smaller than four, write(2)  returns  -1  and
                     sets  errno  to  EINVAL.  Otherwise, a four-byte value is
                     copied from the data buffer, updating the  value  of  the
                     specified signal notification register.  The signal noti-
                     fication register will either be replaced with the  input
                     data  or  will  be updated to the bitwise OR operation of
                     the old value and the input data, depending on  the  con-
                     tents  of  the signal1_type or signal2_type files respec-
                     tively.

       /signal1_type, /signal2_type
              These two files change the behavior of the signal1  and  signal2
              notification  files.   They contain a numeric ASCII string which
              is read as either "1" or "0".  In mode 0 (overwrite), the  hard-
              ware  replaces  the contents of the signal channel with the data
              that is written to it.  In mode 1 (logical OR), the hardware ac-
              cumulates  the  bits  that  are subsequently written to it.  The
              possible operations on an open signal1_type or signal2_type file
              are:

              read(2)
                     When  the  count  supplied to the read(2) call is shorter
                     than the required length for the digit  (plus  a  newline
                     character),  subsequent reads from the same file descrip-
                     tor will complete the string.  When a complete string has
                     been  read,  all  subsequent  read operations will return
                     zero bytes and a new file descriptor needs to  be  opened
                     to read the value again.

              write(2)
                     A write(2) operation on the file sets the register to the
                     value given in the string.  The string is parsed from the
                     beginning until the first nonnumeric character or the end
                     of the buffer.  Subsequent writes to the  same  file  de-
                     scriptor overwrite the previous setting.

       /mbox_info, /ibox_info, /wbox_info, /dma_into, /proxydma_info
              Read-only  files  that  contain the saved state of the SPU mail-
              boxes and DMA queues.  This allows the  SPU  status  to  be  in-
              spected,  mainly  for  debugging.   The  mbox_info and ibox_info
              files each contain the four-byte mailbox message that  has  been
              written  by  the  SPU.   If no message has been written to these
              mailboxes, then contents  of  these  files  is  undefined.   The
              mbox_stat,  ibox_stat  and wbox_stat files contain the available
              message count.

              The wbox_info file contains an array of four-byte  mailbox  mes-
              sages,  which  have been sent to the SPU.  With current CBEA ma-
              chines, the array is four items in length, so up to 4 * 4  =  16
              bytes can be read from this file.  If any mailbox queue entry is
              empty, then the bytes read at the corresponding location are un-
              defined.

              The  dma_info  file  contains  the  contents  of the SPU MFC DMA
              queue, represented as the following structure:

                  struct spu_dma_info {
                      uint64_t         dma_info_type;
                      uint64_t         dma_info_mask;
                      uint64_t         dma_info_status;
                      uint64_t         dma_info_stall_and_notify;
                      uint64_t         dma_info_atomic_command_status;
                      struct mfc_cq_sr dma_info_command_data[16];
                  };

              The last member of this data structure is the actual DMA  queue,
              containing 16 entries.  The mfc_cq_sr structure is defined as:

                  struct mfc_cq_sr {
                      uint64_t mfc_cq_data0_RW;
                      uint64_t mfc_cq_data1_RW;
                      uint64_t mfc_cq_data2_RW;
                      uint64_t mfc_cq_data3_RW;
                  };

              The  proxydma_info  file  contains  similar information, but de-
              scribes the proxy DMA queue (i.e., DMAs  initiated  by  entities
              outside the SPU) instead.  The file is in the following format:

                  struct spu_proxydma_info {
                      uint64_t         proxydma_info_type;
                      uint64_t         proxydma_info_mask;
                      uint64_t         proxydma_info_status;
                      struct mfc_cq_sr proxydma_info_command_data[8];
                  };

              Accessing these files requires that the SPU context is scheduled
              out - frequent use can be inefficient.  These files  should  not
              be used for normal program operation.

              These  files  are not present on contexts that have been created
              with the SPU_CREATE_NOSCHED flag.

       /cntl  This file provides access to the SPU Run Control and SPU  status
              registers,  as  an  ASCII  string.  The following operations are
              supported:

              read(2)
                     Reads from the cntl file will return an ASCII string with
                     the hex value of the SPU Status register.

              write(2)
                     Writes  to  the  cntl file will set the context's SPU Run
                     Control register.

       /mfc   Provides access to the Memory Flow Controller of the SPU.  Read-
              ing from the file returns the contents of the SPU's MFC Tag Sta-
              tus register, and writing to the file initiates a DMA  from  the
              MFC.  The following operations are supported:

              write(2)
                     Writes to this file need to be in the format of a MFC DMA
                     command, defined as follows:

                         struct mfc_dma_command {
                             int32_t  pad;    /* reserved */
                             uint32_t lsa;    /* local storage address */
                             uint64_t ea;     /* effective address */
                             uint16_t size;   /* transfer size */
                             uint16_t tag;    /* command tag */
                             uint16_t class;  /* class ID */
                             uint16_t cmd;    /* command opcode */
                         };

                     Writes  are  required   to   be   exactly   sizeof(struct
                     mfc_dma_command) bytes in size.  The command will be sent
                     to the SPU's MFC proxy queue, and the tag stored  in  the
                     kernel (see below).

              read(2)
                     Reads  the  contents  of the tag status register.  If the
                     file is opened in blocking  mode  (i.e.,  without  O_NON-
                     BLOCK), then the read will block until a DMA tag (as per-
                     formed by a previous write) is complete.  In  nonblocking
                     mode,  the MFC tag status register will be returned with-
                     out waiting.

              poll(2)
                     Calling poll(2) on the mfc file will block  until  a  new
                     DMA  can  be started (by checking for POLLOUT) or until a
                     previously started DMA (by checking for POLLIN) has  been
                     completed.

                     /mss  Provides access to the MFC MultiSource Synchroniza-
                     tion (MSS) facility.  By mmap(2)-ing this file, processes
                     can access the MSS area of the SPU.

                     The following operations are supported:

              mmap(2)
                     Mapping  mss  into the process address space gives access
                     to the SPU MSS area within  the  process  address  space.
                     Only MAP_SHARED mappings are allowed.

       /psmap Provides  access  to the whole problem-state mapping of the SPU.
              Applications can use this area to interface to the  SPU,  rather
              than writing to individual register files in spufs.

              The following operations are supported:

              mmap(2)
                     Mapping  psmap  gives  a  process a direct map of the SPU
                     problem state area.  Only MAP_SHARED  mappings  are  sup-
                     ported.

       /phys-id
              Read-only  file  containing the physical SPU number that the SPU
              context is running on.  When the context is  not  running,  this
              file contains the string "-1".

              The physical SPU number is given by an ASCII hex string.

       /object-id
              Allows  applications  to  store (or retrieve) a single 64-bit ID
              into the context.  This ID is later used by profiling  tools  to
              uniquely identify the context.

              write(2)
                     By  writing  an  ASCII hex value into this file, applica-
                     tions can set the object ID of the SPU context.  Any pre-
                     vious value of the object ID is overwritten.

              read(2)
                     Reading  this file gives an ASCII hex string representing
                     the object ID for this SPU context.

EXAMPLES
       /etc/fstab  entry
              none      /spu      spufs     gid=spu   0    0

SEE ALSO
       close(2), spu_create(2), spu_run(2), capabilities(7)

       The Cell Broadband Engine Architecture (CBEA) specification

COLOPHON
       This page is part of release 5.07 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

Linux                             2020-06-09                          SPUFS(7)

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