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5e6d9f511e
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>
72 lines
2.4 KiB
Plaintext
72 lines
2.4 KiB
Plaintext
/*
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* File: Documentation/blackfin/bfin-gpio-note.txt
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* Based on:
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* Author:
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*
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* Created: $Id: bfin-gpio-note.txt 2008-11-24 16:42 grafyang $
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* Description: This file contains the notes in developing/using bfin-gpio.
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*
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*
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* Rev:
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*
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* Modified:
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* Copyright 2004-2008 Analog Devices Inc.
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*
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* Bugs: Enter bugs at http://blackfin.uclinux.org/
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*
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*/
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1. Blackfin GPIO introduction
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There are many GPIO pins on Blackfin. Most of these pins are muxed to
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multi-functions. They can be configured as peripheral, or just as GPIO,
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configured to input with interrupt enabled, or output.
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For detailed information, please see "arch/blackfin/kernel/bfin_gpio.c",
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or the relevant HRM.
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2. Avoiding resource conflict
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Followed function groups are used to avoiding resource conflict,
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- Use the pin as peripheral,
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int peripheral_request(unsigned short per, const char *label);
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int peripheral_request_list(const unsigned short per[], const char *label);
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void peripheral_free(unsigned short per);
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void peripheral_free_list(const unsigned short per[]);
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- Use the pin as GPIO,
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int bfin_gpio_request(unsigned gpio, const char *label);
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void bfin_gpio_free(unsigned gpio);
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- Use the pin as GPIO interrupt,
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int bfin_gpio_irq_request(unsigned gpio, const char *label);
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void bfin_gpio_irq_free(unsigned gpio);
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The request functions will record the function state for a certain pin,
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the free functions will clear it's function state.
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Once a pin is requested, it can't be requested again before it is freed by
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previous caller, otherwise kernel will dump stacks, and the request
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function fail.
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These functions are wrapped by other functions, most of the users need not
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care.
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3. But there are some exceptions
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- Kernel permit the identical GPIO be requested both as GPIO and GPIO
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interrut.
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Some drivers, like gpio-keys, need this behavior. Kernel only print out
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warning messages like,
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bfin-gpio: GPIO 24 is already reserved by gpio-keys: BTN0, and you are
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configuring it as IRQ!
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Note: Consider the case that, if there are two drivers need the
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identical GPIO, one of them use it as GPIO, the other use it as
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GPIO interrupt. This will really cause resource conflict. So if
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there is any abnormal driver behavior, please check the bfin-gpio
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warning messages.
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- Kernel permit the identical GPIO be requested from the same driver twice.
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