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Commit 5e6d9f511e0188d34fa7a93ce2d0e6194442b0da

Authored by Graf Yang
Committed by Bryan Wu
1 parent d1a853057a
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

Blackfin arch: Add document about bfin-gpio 

Add document about bfin-gpio when requesting a pin
both as gpio and gpio interrupt.

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

Showing 2 changed files with 74 additions and 0 deletions Side-by-side Diff

Documentation/blackfin/00-INDEX
Diff comments   View file @ 5e6d9f5
... ... @@ -9,4 +9,7 @@
9 9  
10 10 Filesystems
11 11 - Requirements for mounting the root file system.
  12 +
  13 +bfin-gpio-note.txt
  14 + - Notes in developing/using bfin-gpio driver.
Documentation/blackfin/bfin-gpio-notes.txt
Diff comments   View file @ 5e6d9f5
  1 +/*
  2 + * File: Documentation/blackfin/bfin-gpio-note.txt
  3 + * Based on:
  4 + * Author:
  5 + *
  6 + * Created: $Id: bfin-gpio-note.txt 2008-11-24 16:42 grafyang $
  7 + * Description: This file contains the notes in developing/using bfin-gpio.
  8 + *
  9 + *
  10 + * Rev:
  11 + *
  12 + * Modified:
  13 + * Copyright 2004-2008 Analog Devices Inc.
  14 + *
  15 + * Bugs: Enter bugs at http://blackfin.uclinux.org/
  16 + *
  17 + */
  18 +
  19 +
  20 +1. Blackfin GPIO introduction
  21 +
  22 + There are many GPIO pins on Blackfin. Most of these pins are muxed to
  23 + multi-functions. They can be configured as peripheral, or just as GPIO,
  24 + configured to input with interrupt enabled, or output.
  25 +
  26 + For detailed information, please see "arch/blackfin/kernel/bfin_gpio.c",
  27 + or the relevant HRM.
  28 +
  29 +
  30 +2. Avoiding resource conflict
  31 +
  32 + Followed function groups are used to avoiding resource conflict,
  33 + - Use the pin as peripheral,
  34 + int peripheral_request(unsigned short per, const char *label);
  35 + int peripheral_request_list(const unsigned short per[], const char *label);
  36 + void peripheral_free(unsigned short per);
  37 + void peripheral_free_list(const unsigned short per[]);
  38 + - Use the pin as GPIO,
  39 + int bfin_gpio_request(unsigned gpio, const char *label);
  40 + void bfin_gpio_free(unsigned gpio);
  41 + - Use the pin as GPIO interrupt,
  42 + int bfin_gpio_irq_request(unsigned gpio, const char *label);
  43 + void bfin_gpio_irq_free(unsigned gpio);
  44 +
  45 + The request functions will record the function state for a certain pin,
  46 + the free functions will clear it's function state.
  47 + Once a pin is requested, it can't be requested again before it is freed by
  48 + previous caller, otherwise kernel will dump stacks, and the request
  49 + function fail.
  50 + These functions are wrapped by other functions, most of the users need not
  51 + care.
  52 +
  53 +
  54 +3. But there are some exceptions
  55 + - Kernel permit the identical GPIO be requested both as GPIO and GPIO
  56 + interrut.
  57 + Some drivers, like gpio-keys, need this behavior. Kernel only print out
  58 + warning messages like,
  59 + bfin-gpio: GPIO 24 is already reserved by gpio-keys: BTN0, and you are
  60 +configuring it as IRQ!
  61 +
  62 + Note: Consider the case that, if there are two drivers need the
  63 + identical GPIO, one of them use it as GPIO, the other use it as
  64 + GPIO interrupt. This will really cause resource conflict. So if
  65 + there is any abnormal driver behavior, please check the bfin-gpio
  66 + warning messages.
  67 +
  68 + - Kernel permit the identical GPIO be requested from the same driver twice.