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

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Date:	Mon, 9 Feb 2009 14:29:15 +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

Sorry, I added CC.

2009/2/9 David Brownell <david-b@...bell.net>:
> On Sunday 08 February 2009, Joonyoung Shim wrote:
>> I have knew if gpio pin is configured as an output, the value of the
>> corresponding bit
>> in the GPIO_DATAOUT register is driven on the corresponding gpio pin.
>> But the implemented API only reports the value of the corresponding bit in the
>> GPIO_DATAIN register. This can report a wrong value.
>>
>> For example, even though the gpio 141pin is configured as an output and assigns
>> the gpio's value to 1 through gpio_set_value(), the result of
>> "# cat /sys/kernel/debug/gpio" reports to me as follows.
>>
>> GPIOs 128-159, gpio:
>>  gpio-141 (motor enable        ) out lo
>>
>> but it should have reported "hi" instead of "lo".
>
> I happen to observe that mach-omap2/mux.c there are a bunch
> of pins that are wrongly multiplexed.  Like:
>
> MUX_CFG_34XX("AE6_34XX_GPIO141", 0x16e,
>                OMAP34XX_MUX_MODE4 | OMAP34XX_PIN_OUTPUT)

I think that it is right because i want to use gpio141 pin as output,

>
> 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.

the reason as i say at former email, is because __omap_get_gpio_datain()
called by gpio_get() of arch/arm/plat-omap/gpio.c reports only value of
OMAP24XX_GPIO_DATAIN register.

- Joonyoung

>
> - Dave
>
>
>
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