linux-kernel - Re: [PATCH] OMAP3 GPIO: Fix getting the value of the GPIO output pin

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Date:	Mon, 9 Feb 2009 21:19:48 +0900
From:	Joonyoung Shim <dofmind@...il.com>
To:	David Brownell <david-b@...bell.net>
Cc:	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	Tony Lindgren <tony@...mide.com>, kyungmin.park@...sung.com
Subject: Re: [PATCH] OMAP3 GPIO: Fix getting the value of the GPIO output pin

2009/2/9 David Brownell <david-b@...bell.net>:
> On Sunday 08 February 2009, Joonyoung Shim wrote:
>> > Which should clearly be AE6_34XX_GPIO141_OUT since it does
>> > not enable the input driver.  Try making that ...PIN_OUTPUT
>> > read ...PIN_INPUT and see if things behave.
>>
>> Of course, it will be better if the name is clear as AE6_34XX_GPIO141_OUT.
>> but, the core of this problem is not it, the chip->get() called in
>> gpiolib_dbg_show()
>> of drivers/gpio/gpiolib.c or dbg_gpio_show() of arch/arm/plat-omap/gpio.c
>> can return the wrong value when gpio pin is configured as an output.
>
> No, the core of the problem is that you're using a GPIO
> which is explicitly configured as output-only ... but are
> treating it as if it were a normal bi-directional GPIO.
>
> It's acting *exactly* right for an output-only GPIO.  But
> that's not the behavior you expect, or want.
>
> If you weren't disabling the input driver, then when you
> ask for the input value it would work as you expect.  Which
> is why I suggested you change how that ball is configured.
> (That's actually a bugfix to those muxing tables ...)

I understood that you say, ths PIN_OUTPUT flag must use
when GPIO pin is output-only, and i got the result i want
after GPIO pin is configured as bi-diretional GPIO.

But i wonder why don't control in gpio_get() of arch/arm/plat-omap/gpio.c
when the GPIO pin is output-only?

thank you.

- Joonyoung

>
> - Dave
>
> p.s. This specific confusion is new on OMAP3; previous
>     OMAPs didn't have the extra byte of options to
>     configure.  The PIN_INPUT flag was, on previous
>     chips, effectively hard-wired on for GPIOs.
>
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