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authorLinus Torvalds <torvalds@linux-foundation.org>2016-07-27 23:58:31 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2016-07-27 23:58:31 +0200
commitff9a082fda424257976f08fce942609f358015e0 (patch)
tree478e6b449b19baaf842369a13923499ce83ef895 /Documentation/video4linux/cx2341x/fw-calling.txt
parentMerge tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi (diff)
parentMerge branch 'topic/docs-next' into v4l_for_linus (diff)
downloadlinux-ff9a082fda424257976f08fce942609f358015e0.tar.xz
linux-ff9a082fda424257976f08fce942609f358015e0.zip
Merge tag 'media/v4.8-4' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
Pull media documentation updates from Mauro Carvalho Chehab: "This patch series does the conversion of all media documentation stuff to Restrutured Text markup format and add them to the Documentation/index.rst file. The media documentation was grouped into 4 books: - media uAPI - media kAPI - V4L driver-specific documentation - DVB driver-specific documentation It also contains several documentation improvements and one fixup patch for a core issue with cropcap. PS. After this patch series, the media DocBook is deprecated and should be removed. I'll add such patch on a future pull request" * tag 'media/v4.8-4' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (322 commits) [media] cx23885-cardlist.rst: add a new card [media] doc-rst: add some needed escape codes [media] doc-rst: kapi: use :c:func: instead of :cpp:func doc-rst: kernel-doc: fix a change introduced by mistake [media] v4l2-ioctl.h add debug info for struct v4l2_ioctl_ops [media] dvb_ringbuffer.h: some documentation improvements [media] v4l2-ctrls.h: fully document the header file [media] doc-rst: Fix some typedef ugly warnings [media] doc-rst: reorganize the kAPI v4l2 chapters [media] rename v4l2-framework.rst to v4l2-intro.rst [media] move V4L2 clocks to a separate .rst file [media] v4l2-fh.rst: add cross references and markups [media] v4l2-fh.rst: add fh contents from v4l2-framework.rst [media] v4l2-fh.h: add documentation for it [media] v4l2-event.rst: add cross-references and markups [media] v4l2-event.h: document all functions [media] v4l2-event.rst: add text from v4l2-framework.rst [media] v4l2-framework.rst: remove videobuf quick chapter [media] v4l2-dev: add cross-references and improve markup [media] doc-rst: move v4l2-dev doc to a separate file ...
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-This page describes how to make calls to the firmware api.
-
-How to call
-===========
-
-The preferred calling convention is known as the firmware mailbox. The
-mailboxes are basically a fixed length array that serves as the call-stack.
-
-Firmware mailboxes can be located by searching the encoder and decoder memory
-for a 16 byte signature. That signature will be located on a 256-byte boundary.
-
-Signature:
-0x78, 0x56, 0x34, 0x12, 0x12, 0x78, 0x56, 0x34,
-0x34, 0x12, 0x78, 0x56, 0x56, 0x34, 0x12, 0x78
-
-The firmware implements 20 mailboxes of 20 32-bit words. The first 10 are
-reserved for API calls. The second 10 are used by the firmware for event
-notification.
-
- Index Name
- ----- ----
- 0 Flags
- 1 Command
- 2 Return value
- 3 Timeout
- 4-19 Parameter/Result
-
-
-The flags are defined in the following table. The direction is from the
-perspective of the firmware.
-
- Bit Direction Purpose
- --- --------- -------
- 2 O Firmware has processed the command.
- 1 I Driver has finished setting the parameters.
- 0 I Driver is using this mailbox.
-
-
-The command is a 32-bit enumerator. The API specifics may be found in the
-fw-*-api.txt documents.
-
-The return value is a 32-bit enumerator. Only two values are currently defined:
-0=success and -1=command undefined.
-
-There are 16 parameters/results 32-bit fields. The driver populates these fields
-with values for all the parameters required by the call. The driver overwrites
-these fields with result values returned by the call. The API specifics may be
-found in the fw-*-api.txt documents.
-
-The timeout value protects the card from a hung driver thread. If the driver
-doesn't handle the completed call within the timeout specified, the firmware
-will reset that mailbox.
-
-To make an API call, the driver iterates over each mailbox looking for the
-first one available (bit 0 has been cleared). The driver sets that bit, fills
-in the command enumerator, the timeout value and any required parameters. The
-driver then sets the parameter ready bit (bit 1). The firmware scans the
-mailboxes for pending commands, processes them, sets the result code, populates
-the result value array with that call's return values and sets the call
-complete bit (bit 2). Once bit 2 is set, the driver should retrieve the results
-and clear all the flags. If the driver does not perform this task within the
-time set in the timeout register, the firmware will reset that mailbox.
-
-Event notifications are sent from the firmware to the host. The host tells the
-firmware which events it is interested in via an API call. That call tells the
-firmware which notification mailbox to use. The firmware signals the host via
-an interrupt. Only the 16 Results fields are used, the Flags, Command, Return
-value and Timeout words are not used.
-