| Graf Yang | 5e6d9f5 | 2009-01-07 23:14:38 +0800 | [diff] [blame] | 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. |
| 69 | |
| 70 | |
| 71 | |