[U-Boot] [PATCH RESEND] gpio: spear_gpio: Fix gpio_set_value() implementation

[Axel Lin]

2013/9/14 Albert ARIBAUD <albert.u.boot at aribaud.net>:
> Hi Axel,
>
> On Fri, 06 Sep 2013 14:22:40 +0800, Axel Lin <axel.lin at ingics.com>
> wrote:
>
>> In current gpio_set_value() implementation, it always sets the gpio control bit
>> no matter the value argument is 0 or 1. Thus the GPIOs never set to low.
>> This patch fixes this bug.
>>
>> Signed-off-by: Axel Lin <axel.lin at ingics.com>
>> Acked-by: Stefan Roese <sr at denx.de>
>> Reviewed-by: Vipin Kumar <vipin.kumar at st.com>
>> ---
>> This patch was sent on http://lists.denx.de/pipermail/u-boot/2013-June/156861.html
>>
>> Has Stefan's Ack:
>> http://lists.denx.de/pipermail/u-boot/2013-June/156864.html
>>
>> Vipin says the code is fine, so I add Vipin's review-by.
>> http://lists.denx.de/pipermail/u-boot/2013-June/156966.html
>>
>> Michael confirms it works:
>> http://lists.denx.de/pipermail/u-boot/2013-August/160652.html
>>
>> No body picks up this patch, so here is a resend.
>> Although I think this is a bug fix, but I'll let maintainers to determinate
>> if this is the material for v2013.10.
>> Anyway, can someone at least let me know if this patch is ok for apply at some
>> point? I have no idea who is maintaining this file.
>>
>> Regards,
>> Axel
>>
>>  drivers/gpio/spear_gpio.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpio/spear_gpio.c b/drivers/gpio/spear_gpio.c
>> index 367b670..6fb4117 100644
>> --- a/drivers/gpio/spear_gpio.c
>> +++ b/drivers/gpio/spear_gpio.c
>> @@ -36,7 +36,10 @@ int gpio_set_value(unsigned gpio, int value)
>>  {
>>       struct gpio_regs *regs = (struct gpio_regs *)CONFIG_GPIO_BASE;
>>
>> -     writel(1 << gpio, &regs->gpiodata[DATA_REG_ADDR(gpio)]);
>> +     if (value)
>> +             writel(1 << gpio, &regs->gpiodata[DATA_REG_ADDR(gpio)]);
>> +     else
>> +             writel(0, &regs->gpiodata[DATA_REG_ADDR(gpio)]);
>>
>>       return 0;
>>  }
>
> Despite discussions in the previous thread and the confirmations that
> this code is functionally equivalent to the Linux code, I still believe
> this code is incorrect for both writing and reading.
>
> From the doc, writing to GPIODATA will obviously copy each of bits 7
> to 0 of the written value into the actuals GPIO mapped to bits 7 to
> 0 of this register (assuming they are configured as outputs, of course).
> Based on this, the code above:
>
> - when setting a single GPIO, sets *but clears up to seven other GPIOs*;
> - when clearing a single GPIO, clears it *and up to seven other GPIOs*.
>
> This code may have been tested only for a single active GPIO at a time,
> for which this code would behave correctly; but as soon as two GPIOs
> from the same bank must be set at the same time, it fails.
>
> Please fix this code so that setting or clearing a GPIO does not set or
> clear any other GPIO, and perform an actual test to confirm this works
> before submitting V2.

No.
Some people (Marek, and *Michael*) asked this question in original
discussion thread.
The datasheet says each GPIO is controlled by *different* register.
(Well, it's unusual.)
And that is why we don't need a read-write-update operation.
Simply write 0 to the register does work. ( *Michael* replied it works )

>
> BTW: if (as the previous thread seemed to imply) no one around has the
> hardware to test this change, then why exactly is it needed?
>
> Amicalement,
> --
> Albert.