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Documentation / video4linux / cx2341x / fw-calling.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

1	This page describes how to make calls to the firmware api.
2	
3	How to call
4	===========
5	
6	The preferred calling convention is known as the firmware mailbox. The
7	mailboxes are basically a fixed length array that serves as the call-stack.
8	
9	Firmware mailboxes can be located by searching the encoder and decoder memory
10	for a 16 byte signature. That signature will be located on a 256-byte boundary.
11	
12	Signature:
13	0x78, 0x56, 0x34, 0x12, 0x12, 0x78, 0x56, 0x34,
14	0x34, 0x12, 0x78, 0x56, 0x56, 0x34, 0x12, 0x78
15	
16	The firmware implements 20 mailboxes of 20 32-bit words. The first 10 are
17	reserved for API calls. The second 10 are used by the firmware for event
18	notification.
19	
20	  Index  Name
21	  -----  ----
22	  0      Flags
23	  1      Command
24	  2      Return value
25	  3      Timeout
26	  4-19   Parameter/Result
27	
28	
29	The flags are defined in the following table. The direction is from the
30	perspective of the firmware.
31	
32	  Bit  Direction  Purpose
33	  ---  ---------  -------
34	  2    O          Firmware has processed the command.
35	  1    I          Driver has finished setting the parameters.
36	  0    I          Driver is using this mailbox.
37	
38	
39	The command is a 32-bit enumerator. The API specifics may be found in the
40	fw-*-api.txt documents.
41	
42	The return value is a 32-bit enumerator. Only two values are currently defined:
43	0=success and -1=command undefined.
44	
45	There are 16 parameters/results 32-bit fields. The driver populates these fields
46	with values for all the parameters required by the call. The driver overwrites
47	these fields with result values returned by the call. The API specifics may be
48	found in the fw-*-api.txt documents.
49	
50	The timeout value protects the card from a hung driver thread. If the driver
51	doesn't handle the completed call within the timeout specified, the firmware
52	will reset that mailbox.
53	
54	To make an API call, the driver iterates over each mailbox looking for the
55	first one available (bit 0 has been cleared). The driver sets that bit, fills
56	in the command enumerator, the timeout value and any required parameters. The
57	driver then sets the parameter ready bit (bit 1). The firmware scans the
58	mailboxes for pending commands, processes them, sets the result code, populates
59	the result value array with that call's return values and sets the call
60	complete bit (bit 2). Once bit 2 is set, the driver should retrieve the results
61	and clear all the flags. If the driver does not perform this task within the
62	time set in the timeout register, the firmware will reset that mailbox.
63	
64	Event notifications are sent from the firmware to the host. The host tells the
65	firmware which events it is interested in via an API call. That call tells the
66	firmware which notification mailbox to use. The firmware signals the host via
67	an interrupt. Only the 16 Results fields are used, the Flags, Command, Return
68	value and Timeout words are not used.
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