linux-kernel - Re: [PATCH] twl4030-gpio: Fix getting the value of the TWL4030 GPIO output pin

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Date:	Wed, 11 Feb 2009 18:16:41 -0800
From:	David Brownell <david-b@...bell.net>
To:	Joonyoung Shim <dofmind@...il.com>
Cc:	Tony Lindgren <tony@...mide.com>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org
Subject: Re: [PATCH] twl4030-gpio: Fix getting the value of the TWL4030 GPIO  output pin

On Monday 09 February 2009, Joonyoung Shim wrote:
> but, it doesn't return actual value of the pin if twl4030 GPIO pin is output.

So it would seem that these GPIOs don't support
bidirectional usage.  Documentation/gpio.txt includes:

>>>		However, note that not all platforms can
>>>	read the value of output pins; those that can't
>>>	should always return zero.  

Which is exactly what's happening here, it seems...




> For example, the GPIO13 pin of twl4030 is configured as an output
> using gpio_direction_output() and assigns the GPIO's value to 1
> using gpio_set_value_cansleep(), the result of "# cat /sys/kernel/debug/gpio"
> reports to me as follows.
> 
> GPIOs 192-209, platform/twl4030_gpio, twl4030, can sleep:
>  gpio-205 (keyled              ) out lo
> 
> but it should have reported "hi" instead of "lo".
> 


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