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-/*
- * File: Documentation/blackfin/bfin-gpio-notes.txt
- * Based on:
- * Author:
- *
- * Created: $Id: bfin-gpio-note.txt 2008-11-24 16:42 grafyang $
- * Description: This file contains the notes in developing/using bfin-gpio.
- *
- *
- * Rev:
- *
- * Modified:
- * Copyright 2004-2008 Analog Devices Inc.
- *
- * Bugs: Enter bugs at http://blackfin.uclinux.org/
- *
- */
-
-
-1. Blackfin GPIO introduction
-
- There are many GPIO pins on Blackfin. Most of these pins are muxed to
- multi-functions. They can be configured as peripheral, or just as GPIO,
- configured to input with interrupt enabled, or output.
-
- For detailed information, please see "arch/blackfin/kernel/bfin_gpio.c",
- or the relevant HRM.
-
-
-2. Avoiding resource conflict
-
- Followed function groups are used to avoiding resource conflict,
- - Use the pin as peripheral,
- int peripheral_request(unsigned short per, const char *label);
- int peripheral_request_list(const unsigned short per[], const char *label);
- void peripheral_free(unsigned short per);
- void peripheral_free_list(const unsigned short per[]);
- - Use the pin as GPIO,
- int bfin_gpio_request(unsigned gpio, const char *label);
- void bfin_gpio_free(unsigned gpio);
- - Use the pin as GPIO interrupt,
- int bfin_gpio_irq_request(unsigned gpio, const char *label);
- void bfin_gpio_irq_free(unsigned gpio);
-
- The request functions will record the function state for a certain pin,
- the free functions will clear its function state.
- Once a pin is requested, it can't be requested again before it is freed by
- previous caller, otherwise kernel will dump stacks, and the request
- function fail.
- These functions are wrapped by other functions, most of the users need not
- care.
-
-
-3. But there are some exceptions
- - Kernel permit the identical GPIO be requested both as GPIO and GPIO
- interrupt.
- Some drivers, like gpio-keys, need this behavior. Kernel only print out
- warning messages like,
- bfin-gpio: GPIO 24 is already reserved by gpio-keys: BTN0, and you are
-configuring it as IRQ!
-
- Note: Consider the case that, if there are two drivers need the
- identical GPIO, one of them use it as GPIO, the other use it as
- GPIO interrupt. This will really cause resource conflict. So if
- there is any abnormal driver behavior, please check the bfin-gpio
- warning messages.
-
- - Kernel permit the identical GPIO be requested from the same driver twice.
-
-
-