.\" Copyright (c) International Business Machines Corp., 2006

.\"

.\" %%%LICENSE_START(GPLv2+_SW_3_PARA)

.\" This program is free software; you can redistribute it and/or

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.\"

.\" HISTORY:

.\" 2005-09-28, created by Arnd Bergmann <arndb@de.ibm.com>,

.\"   Mark Nutter <mnutter@us.ibm.com> and

.\"   Ulrich Weigand <Ulrich.Weigand@de.ibm.com>

.\" 2006-06-16, revised by Eduardo M. Fleury <efleury@br.ibm.com>

.\" 2007-07-10, quite a lot of polishing by mtk

.\" 2007-09-28, updates for newer kernels by Jeremy Kerr <jk@ozlabs.org>

.\"

.TH SPUFS 7 2017-09-15 Linux "Linux Programmer's Manual"

.SH NAME

spufs \- SPU filesystem

.SH DESCRIPTION

The SPU filesystem is used on PowerPC machines that implement the

Cell Broadband Engine Architecture in order to access Synergistic

Processor Units (SPUs).

.PP

The filesystem provides a name space similar to POSIX shared

memory or message queues.

Users that have write permissions

on the filesystem can use

.BR spu_create (2)

to establish SPU contexts under the

.B spufs

root directory.

.PP

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.

.SS Mount options

.TP

.B uid=<uid>

Set the user owning the mount point; the default is 0 (root).

.TP

.B gid=<gid>

Set the group owning the mount point; the default is 0 (root).

.TP

.B mode=<mode>

Set the mode of the top-level directory in

.BR spufs ,

as an octal mode string.

The default is 0775.

.SS Files

The files in

.B spufs

mostly follow the standard behavior for regular system calls like

.BR read (2)

or

.BR 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.

.PP

All files that support the

.BR read (2)

operation also support

.BR readv (2)

and all files that support the

.BR write (2)

operation also support

.BR writev (2).

All files support the

.BR access (2)

and

.BR stat (2)

family of operations, but for the latter call,

the only fields of the returned

.I stat

structure that contain reliable information are

.IR st_mode ,

.IR st_nlink ,

.IR st_uid ,

and

.IR st_gid .

.PP

All files support the

.BR chmod (2)/ fchmod (2)

and

.BR chown (2)/ fchown (2)

operations, but will not be able to grant permissions that contradict

the possible operations (e.g., read access on the

.I wbox

file).

.PP

The current set of files is:

.TP

.I /capabilities

Contains a comma-delimited string representing the capabilities of this

SPU context.

Possible capabilities are:

.RS

.TP

.B sched

This context may be scheduled.

.TP

.B step

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

.PP

New capabilities flags may be added in the future.

.RE

.TP

.I /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

.I mem

file are:

.RS

.TP

.BR read "(2), " pread "(2), " write "(2), " pwrite "(2), " lseek (2)

These operate as usual, with the exception that

.BR lseek (2),

.BR write (2),

and

.BR 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.

.TP

.BR mmap (2)

Mapping

.I mem

into the process address space provides access to the SPU local

storage within the process address space.

Only

.B MAP_SHARED

mappings are allowed.

.RE

.TP

.I /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.

.IP

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.

.IP

The

.I regs

file is not present on contexts that have been created with the

.B SPU_CREATE_NOSCHED

flag.

.TP

.I /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

.BR poll (2)

cannot be used to block on this file.

The only possible operation on an open

.I mbox

file is:

.RS

.TP

.BR read (2)

If

.I count

is smaller than four,

.BR read (2)

returns \-1 and sets

.I errno

to

.BR 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

.I errno

is set to

.BR EAGAIN .

When data

has been read successfully, four bytes are placed in

the data buffer and the value four is returned.

.RE

.TP

.I /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

.BR read (2)

on an open

.I ibox

file will block until the SPU has written data to its interrupt mailbox

channel (unless the file has been opened with

.BR O_NONBLOCK ,

see below).

Also,

.BR poll (2)

and similar system calls can be used to monitor for the presence

of mailbox data.

.IP

The possible operations on an open

.I ibox

file are:

.RS

.TP

.BR read (2)

If

.I count

is smaller than four,

.BR read (2)

returns \-1 and sets

.I errno

to

.BR EINVAL .

If there is no data available in the mailbox and the file

descriptor has been opened with

.BR O_NONBLOCK ,

the return value is set to \-1 and

.I errno

is set to

.BR EAGAIN .

.IP

If there is no data available in the mailbox and the file

descriptor has been opened without

.BR 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.

.TP

.BR poll (2)

Poll on the

.I ibox

file returns

.I "(POLLIN | POLLRDNORM)"

whenever data is available for reading.

.RE

.TP

.I /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,

.BR write (2)

will block, and

.BR poll (2)

can be used to block until the mailbox is available for writing again.

The possible operations on an open

.I wbox

file are:

.RS

.TP

.BR write (2)

If

.I count

is smaller than four,

.BR write (2)

returns \-1 and sets

.I errno

to

.BR EINVAL .

If there is no space available in the mailbox and the file

descriptor has been opened with

.BR O_NONBLOCK ,

the return

value is set to \-1 and

.I errno

is set to

.BR EAGAIN .

.IP

If there is no space available in the mailbox and the file

descriptor has been opened without

.BR 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.

.TP

.BR poll (2)

A poll on the

.I wbox

file returns

.I "(POLLOUT | POLLWRNORM)"

whenever space is available for writing.

.RE

.TP

.IR /mbox_stat ", " /ibox_stat ", " /wbox_stat

These are read-only files that contain the length of the current

queue of each mailbox\(emthat is, how many words can be read from

.IR mbox " or " ibox

or how many words can be written to

.I 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

.I *box_stat

file is:

.RS

.TP

.BR read (2)

If

.I count

is smaller than four,

.BR read (2)

returns \-1 and sets

.I errno

to

.BR 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

.IR mbox_stat

and

.IR ibox_stat )

or written to (for

.IR wbox_stat )

the respective mailbox without blocking or returning an

.BR EAGAIN

error.

.RE

.TP

.IR /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

.IR npc ,

see below) require that the SPU context be scheduled out,

so frequent access to

these files is not recommended for normal program operation.

.IP

The contents of these files are:

.RS

.TP 16

.I npc

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

.TP

.I decr

SPU Decrementer

.TP

.I decr_status

Decrementer Status

.TP

.I spu_tag_mask

MFC tag mask for SPU DMA

.TP

.I event_mask

Event mask for SPU interrupts

.TP

.I event_status

Number of SPU events pending (read-only)

.TP

.I srr0

Interrupt Return address register

.TP

.I lslr

Local Store Limit Register

.RE

.IP

The possible operations on these files are:

.RS

.TP

.BR read (2)

Reads the current register value.

If the register value is larger than the buffer passed to the

.BR read (2)

system call, subsequent reads will continue reading from the same

buffer, until the end of the buffer is reached.

.IP

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.

.TP

.BR write (2)

A

.BR 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.

.IP

Except for the

.I npc

file, these files are not present on contexts that have been created with

the

.B SPU_CREATE_NOSCHED

flag.

.RE

.TP

.IR /fpcr

This file provides access to the Floating Point Status and

Control Register (fcpr) as a binary, four-byte file.

The operations on the

.I fpcr

file are:

.RS

.TP

.BR read (2)

If

.I count

is smaller than four,

.BR read (2)

returns \-1 and sets

.I errno

to

.BR EINVAL .

Otherwise, a four-byte value is placed in the data buffer;

this is the current value of the

.I fpcr

register.

.TP

.BR write (2)

If

.I count

is smaller than four,

.BR write (2)

returns \-1 and sets

.I errno

to

.BR EINVAL .

Otherwise, a four-byte value is copied from the data buffer,

updating the value of the

.I fpcr

register.

.RE

.TP

.IR /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

.I signal1

or

.I signal2

file are:

.RS

.TP

.BR read (2)

If

.I count

is smaller than four,

.BR read (2)

returns \-1 and sets

.I errno

to

.BR EINVAL .

Otherwise, a four-byte value is placed in the data buffer;

this is the current value of the specified signal notification

register.

.TP

.BR write (2)

If

.I count

is smaller than four,

.BR write (2)

returns \-1 and sets

.I errno

to

.BR 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

.IR signal1_type

or

.IR signal2_type

files respectively.

.RE

.TP

.IR /signal1_type ", " /signal2_type

These two files change the behavior of the

.IR signal1

and

.IR 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

.I signal1_type

or

.I signal2_type

file are:

.RS

.TP

.BR read (2)

When the count supplied to the

.BR 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.

.TP

.BR write (2)

A

.BR 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.

.RE

.TP

.IR /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

.I mbox_info

and

.I 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

.IR mbox_stat ,

.I ibox_stat

and

.I wbox_stat

files contain the available message count.

.IP

The

.I 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.

.IP

The

.I dma_info

file contains the contents of the SPU MFC DMA queue, represented as the

following structure:

.IP

.in +4n

.EX

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];

};

.EE

.in

.IP

The last member of this data structure is the actual DMA queue,

containing 16 entries.

The

.I mfc_cq_sr

structure is defined as:

.IP

.in +4n

.EX

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;

};

.EE

.in

.IP

The

.I 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:

.IP

.in +4n

.EX

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];

};

.EE

.in

.IP

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.

.IP

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

.B SPU_CREATE_NOSCHED

flag.

.TP

.IR /cntl

This file provides access to the SPU Run Control and SPU status

registers, as an ASCII string.

The following operations are supported:

.RS

.TP

.BR read (2)

Reads from the

.I cntl

file will return an ASCII string with the hex

value of the SPU Status register.

.TP

.BR write (2)

Writes to the

.I cntl

file will set the context's SPU Run Control register.

.RE

.TP

.I /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:

.RS

.TP

.BR write (2)

Writes to this file need to be in the format of a MFC DMA command,

defined as follows:

.IP

.in +4n

.EX

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 */

};

.EE

.in

.IP

Writes are required to be exactly

.I 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).

.TP

.BR read (2)

Reads the contents of the tag status register.

If the file is opened in blocking mode (i.e., without

.BR 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.

.TP

.BR poll (2)

Calling

.BR poll (2)

on the

.I mfc

file will block until a new DMA can be

started (by checking for

.BR POLLOUT )

or until a previously started DMA

(by checking for

.BR POLLIN )

has been completed.

.IP

.I /mss

Provides access to the MFC MultiSource Synchronization (MSS) facility.

By

.BR mmap (2)-ing

this file, processes can access the MSS area of the SPU.

.IP

The following operations are supported:

.TP

.BR mmap (2)

Mapping

.B mss

into the process address space gives access to the SPU MSS area

within the process address space.

Only

.B MAP_SHARED

mappings are allowed.

.RE

.TP

.I /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

.BR spufs .

.IP

The following operations are supported:

.RS

.TP

.BR mmap (2)

Mapping

.B psmap

gives a process a direct map of the SPU problem state area.

Only

.B MAP_SHARED

mappings are supported.

.RE

.TP

.I /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".

.IP

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

.TP

.I /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.

.RS

.TP

.BR 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.

.TP

.BR read (2)

Reading this file gives an ASCII hex string representing the object ID

for this SPU context.

.RE

.SH EXAMPLE

.TP

.IR /etc/fstab "  entry"

none  	/spu  	spufs  	gid=spu  	0	0

.\" .SH AUTHORS

.\" Arnd Bergmann <arndb@de.ibm.com>, Mark Nutter <mnutter@us.ibm.com>,

.\" Ulrich Weigand <Ulrich.Weigand@de.ibm.com>, Jeremy Kerr <jk@ozlabs.org>

.SH SEE ALSO

.BR close (2),

.BR spu_create (2),

.BR spu_run (2),

.BR capabilities (7)

.PP

.I The Cell Broadband Engine Architecture (CBEA) specification

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.