spufs(7) — Linux manual page

NAME | DESCRIPTION | EXAMPLES | SEE ALSO | COLOPHON

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

NAME         top

       spufs - SPU filesystem

DESCRIPTION         top

       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 system 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 described 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)
       operations, 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
                     debugging.

              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 operations 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
                     access 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 normal 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 message), 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 returned.

       /ibox  The second SPU-to-CPU communication mailbox.  This file is
              similar 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 (unless 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)
                     whenever 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 return a big-endian binary integer
              number.  The only possible operation 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) require 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 descriptor 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 descriptor
                     overwrite the previous setting.

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

       /fpcr  This file provides access to the Floating Point Status and
              Control Register (fcpr) as a binary, four-byte file.  The
              operations 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 notification 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 contents
                     of the signal1_type or signal2_type files
                     respectively.

       /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 hardware replaces the contents of the
              signal channel with the data that is written to it.  In
              mode 1 (logical OR), the hardware accumulates 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 descriptor 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 descriptor
                     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
              mailboxes and DMA queues.  This allows the SPU status to
              be inspected, 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
              messages, which have been sent to the SPU.  With current
              CBEA machines, 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 undefined.

              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
              describes 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.
              Reading from the file returns the contents of the SPU's
              MFC Tag Status 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_NONBLOCK), then the read will block until a DMA
                     tag (as performed by a previous write) is complete.
                     In nonblocking mode, the MFC tag status register
                     will be returned without 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
                     Synchronization (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 supported.

       /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,
                     applications can set the object ID of the SPU
                     context.  Any previous 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         top

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

SEE ALSO         top

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

       The Cell Broadband Engine Architecture (CBEA) specification

COLOPHON         top

       This page is part of release 5.10 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                          2020-12-21                       SPUFS(7)

Pages that refer to this page: spu_create(2)spu_run(2)