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

[Albert ARIBAUD]

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.

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.