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

[Michael Trimarchi]

Hi

On 06/20/2013 03:56 PM, Axel Lin wrote:
> 2013/6/20 Marek Vasut <ma...@denx.de>
>>
>> Dear Axel Lin,
>>
>>> 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....@ingics.com>
>>> ---
>>>  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 d3c728e..8878608 100644
>>> --- a/drivers/gpio/spear_gpio.c
>>> +++ b/drivers/gpio/spear_gpio.c
>>> @@ -52,7 +52,10 @@ 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)]);
>>
>> How can this possibly work? Writing 0 to the whole bank will unset all the
>> GPIOs, no ?
> 
> 
> Because each GPIO is controlled by a register.
> And only one bit will be set when set gpio to high.
> 

Yes, but how to reset just one bit if you use the same register offset?

I don't know this core but I know two possibilities:

1) one set register and one clear register
        if (enable)
                writel(1 << gpio, REGSET_BANK(gpio));
        else
                writel(1 << gpio, REGCLEAR_BANK(gpio));
2) or 
set operation
        reg = readl(REG(gpio);
        if (enable)
                reg |= 1 << gpio;
        else
                reg &= ~(1 << gpio);
        writel(reg, REG(GPIO));

Any other way?

Michael 
        

> So it's safe to write 0 for clearing the bit.
> 
> Note, the gpio_get_value() implementation also assumes there is only one bit
> will be set. ( If this is not true, both gpio_get_value() and gpio_set_value()
> need fix.)
> 
> Vipin, can you review this patch and confirm this behavior?
> 
> Thanks,
> Axel
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> 


-- 
| Michael Nazzareno Trimarchi                     Amarula Solutions BV |
| COO  -  Founder                                      Cruquiuskade 47 |
| +31(0)851119172                                 Amsterdam 1018 AM NL |


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