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author | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2009-01-08 05:24:38 (GMT) |
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committer | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2009-01-08 05:24:38 (GMT) |
commit | 24f030175d30f019be41766cdf88c2ff03de19ff (patch) | |
tree | 354232a84e82d5a721ed7b1a9af580ff2a59be8f /Documentation/blackfin/bfin-gpio-notes.txt | |
parent | 4aa12f7b927c3cac0e0cf3503642597527d0ece0 (diff) | |
parent | 9e42d0cf5020aaf217433cad1a224745241d212a (diff) | |
download | linux-24f030175d30f019be41766cdf88c2ff03de19ff.tar.xz |
Merge commit 'origin/master' into next
Diffstat (limited to 'Documentation/blackfin/bfin-gpio-notes.txt')
-rw-r--r-- | Documentation/blackfin/bfin-gpio-notes.txt | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/Documentation/blackfin/bfin-gpio-notes.txt b/Documentation/blackfin/bfin-gpio-notes.txt new file mode 100644 index 0000000..9898c7d --- /dev/null +++ b/Documentation/blackfin/bfin-gpio-notes.txt @@ -0,0 +1,71 @@ +/* + * File: Documentation/blackfin/bfin-gpio-note.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 it's 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 + interrut. + 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. + + + |