[U-Boot] [PATCH] gpio: mxc_gpio: Fix gpio_get_value() when the GPIO is an output

[Otavio Salvador]

On Sun, Sep 29, 2013 at 4:49 PM, Otavio Salvador
<otavio at ossystems.com.br> wrote:
> On Sun, Sep 29, 2013 at 4:45 PM, Benoît Thébaudeau
> <benoit.thebaudeau at advansee.com> wrote:
>> On Sunday, September 29, 2013 9:42:44 PM, Otavio Salvador wrote:
>>> On Sun, Sep 29, 2013 at 4:25 PM, Benoît Thébaudeau
>>> <benoit.thebaudeau at advansee.com> wrote:
>>> ...
>>> > Hence, gpio_get_value() should be left unchanged (using PSR in all cases),
>>> > and
>>> > SION should be set for all GPIOs in the i.MX6 pin definition header files.
>>>
>>> I just does not follow why this preferred against Fabio's proposed
>>> patch to read from DR?
>>
>> Because in case of a level conflict between the GPIO output and some other
>> hardware on the board, one would expect gpio_get_value() to return the actual
>> pin level, and not the level that the GPIO output tries (but possibly fails) to
>> apply on this pin.
>
> Ahh now I see. I agree :-)

I sent the patch to fix this adding the flag to the GPIO pins.

I tested it and it works fine indeed. The patch is awaiting for
approval as it is a little big. The commitlog is below for reference:

    mx6: Add IOMUX_CONFIG_SION flag to all GPIO pins

    The IOMUX_CONFIG_SION allows for reading PAD value from PSR register.

    The following quote from the datasheet:

    ,----
    | ...
    | 28.4.2.2 GPIO Write Mode
    | The programming sequence for driving output signals should be as follows:
    | 1. Configure IOMUX to select GPIO mode (Via IOMUXC), also enable
SION if need
    | to read loopback pad value through PSR
    | 2. Configure GPIO direction register to output (GPIO_GDIR[GDIR]
set to 1b).
    | 3. Write value to data register (GPIO_DR).
    | ...
    `----

    This fixes the gpio_get_value to properly work when a GPIO is set for
    output and has no conflicts.

    Thanks for Benoît Thébaudeau <benoit.thebaudeau at advansee.com>, Fabio
    Estevam <fabio.estevam at freescale.com> and Eric Bénard
    <eric at eukrea.com> for helping to properly trace this down.

    Signed-off-by: Otavio Salvador <otavio at ossystems.com.br>

Again, thanks for the help on this.

-- 
Otavio Salvador                             O.S. Systems
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