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authorGraf Yang <graf.yang@analog.com>2009-01-07 23:14:38 +0800
committerBryan Wu <cooloney@kernel.org>2009-01-07 23:14:38 +0800
commit5e6d9f511e0188d34fa7a93ce2d0e6194442b0da (patch)
treebacabdb1365320f3becea3ff0f129cb7d88f280a /Documentation/blackfin
parentd1a853057a13e63c40c9b8715e585af15f1b141a (diff)
downloadlinux-linaro-stable-5e6d9f511e0188d34fa7a93ce2d0e6194442b0da.tar.gz
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 <graf.yang@analog.com> Signed-off-by: Bryan Wu <cooloney@kernel.org>
Diffstat (limited to 'Documentation/blackfin')
-rw-r--r--Documentation/blackfin/00-INDEX3
-rw-r--r--Documentation/blackfin/bfin-gpio-notes.txt71
2 files changed, 74 insertions, 0 deletions
diff --git a/Documentation/blackfin/00-INDEX b/Documentation/blackfin/00-INDEX
index 7cb3b356b249..d6840a91e1e1 100644
--- a/Documentation/blackfin/00-INDEX
+++ b/Documentation/blackfin/00-INDEX
@@ -9,3 +9,6 @@ cachefeatures.txt
Filesystems
- Requirements for mounting the root file system.
+
+bfin-gpio-note.txt
+ - 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
index 000000000000..9898c7ded7d3
--- /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.
+
+
+