|author||Graf Yang <email@example.com>||2009-01-07 23:14:38 +0800|
|committer||Bryan Wu <firstname.lastname@example.org>||2009-01-07 23:14:38 +0800|
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 <email@example.com> Signed-off-by: Bryan Wu <firstname.lastname@example.org>
Diffstat (limited to 'Documentation/blackfin')
2 files changed, 74 insertions, 0 deletions
diff --git a/Documentation/blackfin/00-INDEX b/Documentation/blackfin/00-INDEX
index 7cb3b356b249..d6840a91e1e1 100644
@@ -9,3 +9,6 @@ cachefeatures.txt
- Requirements for mounting the root file system.
+ - Notes in developing/using bfin-gpio driver.
diff --git a/Documentation/blackfin/bfin-gpio-notes.txt b/Documentation/blackfin/bfin-gpio-notes.txt
new file mode 100644
@@ -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
+3. But there are some exceptions
+ - Kernel permit the identical GPIO be requested both as GPIO and GPIO
+ 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.