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Date: Mon, 13 Feb 2012 11:59:47 +0530 From: Laxman Dewangan <ldewangan@...dia.com> To: grant.likely@...retlab.ca, linus.walleij@...ricsson.com, dunlap@...otime.net, lrg@...com, broonie@...nsource.wolfsonmicro.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org Cc: linux-tegra@...r.kernel.org, ldewangan@...dia.com Subject: [PATCH V1 2/3] Documentation: gpio: Add details of open-drain configuration Adding details of open drain configuration of the gpio so that client can set the pin as open drain at the time of gpio request. Signed-off-by: Laxman Dewangan <ldewangan@...dia.com> --- Documentation/gpio.txt | 21 +++++++++++++++++++-- 1 files changed, 19 insertions(+), 2 deletions(-) diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index 792faa3..b08933c 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -302,6 +302,7 @@ where 'flags' is currently defined to specify the following properties: * GPIOF_INIT_LOW - as output, set initial level to LOW * GPIOF_INIT_HIGH - as output, set initial level to HIGH + * GPIOF_OD - gpio pin is open drain type. since GPIOF_INIT_* are only valid when configured as output, so group valid combinations as: @@ -310,8 +311,7 @@ combinations as: * GPIOF_OUT_INIT_LOW - configured as output, initial level LOW * GPIOF_OUT_INIT_HIGH - configured as output, initial level HIGH -In the future, these flags can be extended to support more properties such -as open-drain status. +In the future, these flags can be extended to support more properties. Further more, to ease the claim/release of multiple GPIOs, 'struct gpio' is introduced to encapsulate all three fields as: @@ -641,6 +641,13 @@ and have the following read/write attributes: for "rising" and "falling" edges will follow this setting. + "open_drain" ... reads as either 0 (false) or 1 (true). Write + any nonzero value to make the pin in open drain. + By setting open drain to true, the output can be set + to HIGH by external PULL UP and setting direction to input. + The output will be set to LOW by setting direction to + output with value is 0. + GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (for the controller implementing GPIOs starting at #42) and have the following read-only attributes: @@ -679,6 +686,9 @@ requested using gpio_request(): /* change the polarity of a GPIO node in sysfs */ int gpio_sysfs_set_active_low(unsigned gpio, int value); + /* change the pin to open drain in sysfs */ + int gpio_sysfs_set_open_drain(unsigned gpio, int value); + After a kernel driver requests a GPIO, it may only be made available in the sysfs interface by gpio_export(). The driver can control whether the signal direction may change. This helps drivers prevent userspace code @@ -698,3 +708,10 @@ differences between boards from user space. This only affects the sysfs interface. Polarity change can be done both before and after gpio_export(), and previously enabled poll(2) support for either rising or falling edge will be reconfigured to follow this setting. + +Drivers can use gpio_sysfs_set_open_drain() to enable/disable the open +drain property of that pins. This only affect the sysfs interface. +The flag will be set as open drain if thsi function is called with value +of 1. It is recommended to set the open drain property before setting +the value in output mode so that pin state cn be set properly based +on the value. -- 1.7.1.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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