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Date: From: Mauro Carvalho Chehab <mchehab@infradead.org> There are some docs at V4L/DVB tree that were never included at kernel. This patch includes those docs. Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
70 lines
2.8 KiB
Plaintext
70 lines
2.8 KiB
Plaintext
This page describes how to make calls to the firmware api.
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How to call
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===========
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The preferred calling convention is known as the firmware mailbox. The
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mailboxes are basically a fixed length array that serves as the call-stack.
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Firmware mailboxes can be located by searching the encoder and decoder memory
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for a 16 byte signature. That signature will be located on a 256-byte boundary.
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Signature:
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0x78, 0x56, 0x34, 0x12, 0x12, 0x78, 0x56, 0x34,
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0x34, 0x12, 0x78, 0x56, 0x56, 0x34, 0x12, 0x78
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The firmware implements 20 mailboxes of 20 32-bit words. The first 10 are
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reserved for API calls. The second 10 are used by the firmware for event
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notification.
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Index Name
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----- ----
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0 Flags
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1 Command
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2 Return value
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3 Timeout
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4-19 Parameter/Result
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The flags are defined in the following table. The direction is from the
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perspective of the firmware.
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Bit Direction Purpose
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--- --------- -------
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2 O Firmware has processed the command.
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1 I Driver has finished setting the parameters.
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0 I Driver is using this mailbox.
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The command is a 32-bit enumerator. The API specifics may be found in the
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fw-*-api.txt documents.
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The return value is a 32-bit enumerator. Only two values are currently defined:
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0=success and -1=command undefined.
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There are 16 parameters/results 32-bit fields. The driver populates these fields
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with values for all the parameters required by the call. The driver overwrites
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these fields with result values returned by the call. The API specifics may be
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found in the fw-*-api.txt documents.
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The timeout value protects the card from a hung driver thread. If the driver
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doesn't handle the completed call within the timeout specified, the firmware
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will reset that mailbox.
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To make an API call, the driver iterates over each mailbox looking for the
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first one available (bit 0 has been cleared). The driver sets that bit, fills
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in the command enumerator, the timeout value and any required parameters. The
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driver then sets the parameter ready bit (bit 1). The firmware scans the
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mailboxes for pending commands, processes them, sets the result code, populates
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the result value array with that call's return values and sets the call
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complete bit (bit 2). Once bit 2 is set, the driver should retrieve the results
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and clear all the flags. If the driver does not perform this task within the
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time set in the timeout register, the firmware will reset that mailbox.
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Event notifications are sent from the firmware to the host. The host tells the
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firmware which events it is interested in via an API call. That call tells the
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firmware which notification mailbox to use. The firmware signals the host via
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an interrupt. Only the 16 Results fields are used, the Flags, Command, Return
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value and Timeout words are not used.
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