[PATCH] gpio: tegra: read output value when gpio is set in direction_out

[PATCH] gpio: tegra: read output value when gpio is set in direction_out

[Laxman Dewangan]

Read the output value when gpio is set for the output mode for
gpio_get_value(). Reading input value in direction out does not
give correct value.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
---
 drivers/gpio/gpio-tegra.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/gpio/gpio-tegra.c b/drivers/gpio/gpio-tegra.c
index c7c175a..0fb2ce7 100644
--- a/drivers/gpio/gpio-tegra.c
+++ b/drivers/gpio/gpio-tegra.c
@@ -135,6 +135,12 @@ static void tegra_gpio_set(struct gpio_chip *chip, unsigned offset, int value)
 
 static int tegra_gpio_get(struct gpio_chip *chip, unsigned offset)
 {
+	int bit_val = BIT(GPIO_BIT(offset));
+
+	/* If gpio is in output mode then read from the out value */
+	if (tegra_gpio_readl(GPIO_OE(offset)) & bit_val)
+		return !!(tegra_gpio_readl(GPIO_OUT(offset)) & bit_val);
+
 	return (tegra_gpio_readl(GPIO_IN(offset)) >> GPIO_BIT(offset)) & 0x1;
 }
 
-- 
1.7.1.1

Re: [PATCH] gpio: tegra: read output value when gpio is set in direction_out

[Stephen Warren]

On 11/07/2012 11:27 PM, Laxman Dewangan wrote:
> Read the output value when gpio is set for the output mode for
> gpio_get_value(). Reading input value in direction out does not
> give correct value.

That's an unfortunate HW design, but oh well. Do you have any idea why
reading the input register doesn't work? If you look at the Tegra20 TRM,
page 666 figure 32 "SFIO/GPIO Pin Multiplexing Architecture", there's
not indication that the input path wouldn't work if the output path is
active. Perhaps the issue is in the GPIO module not the pinmux module?

> diff --git a/drivers/gpio/gpio-tegra.c b/drivers/gpio/gpio-tegra.c

>  static int tegra_gpio_get(struct gpio_chip *chip, unsigned offset)
>  {
> +	int bit_val = BIT(GPIO_BIT(offset));
> +
> +	/* If gpio is in output mode then read from the out value */
> +	if (tegra_gpio_readl(GPIO_OE(offset)) & bit_val)
> +		return !!(tegra_gpio_readl(GPIO_OUT(offset)) & bit_val);
> +
>  	return (tegra_gpio_readl(GPIO_IN(offset)) >> GPIO_BIT(offset)) & 0x1;
>  }

Any chance of using the same kind of logic to isolate the bit value? One
branch above does !!(val & mask) and the other (val >> shift) & 1.

Re: [PATCH] gpio: tegra: read output value when gpio is set in direction_out

[Laxman Dewangan]

On Thursday 08 November 2012 10:28 PM, Stephen Warren wrote:
> On 11/07/2012 11:27 PM, Laxman Dewangan wrote:
>> Read the output value when gpio is set for the output mode for
>> gpio_get_value(). Reading input value in direction out does not
>> give correct value.
> That's an unfortunate HW design, but oh well. Do you have any idea why
> reading the input register doesn't work? If you look at the Tegra20 TRM,
> page 666 figure 32 "SFIO/GPIO Pin Multiplexing Architecture", there's
> not indication that the input path wouldn't work if the output path is
> active. Perhaps the issue is in the GPIO module not the pinmux module?
>

I think this is in the gpio controller design. I again check this in 
cardhu wih dumping gpio registers
Bank:Port CNF OE OUT IN INT_STA INT_ENB INT_LVL
2:2       1c  18 08 04 00 00 000000

GPIO pin2,pin3 and pin4 are in gpio mode.
GPIO pin 3 and pin4 are in output mode and pin2 is in input mode.
Set the output to 1 for pin3 and reading back through gpio_in register 
for this pin, it is showing as 0, not 1.


>> diff --git a/drivers/gpio/gpio-tegra.c b/drivers/gpio/gpio-tegra.c
>>   static int tegra_gpio_get(struct gpio_chip *chip, unsigned offset)
>>   {
>> +	int bit_val = BIT(GPIO_BIT(offset));
>> +
>> +	/* If gpio is in output mode then read from the out value */
>> +	if (tegra_gpio_readl(GPIO_OE(offset))&  bit_val)
>> +		return !!(tegra_gpio_readl(GPIO_OUT(offset))&  bit_val);
>> +
>>   	return (tegra_gpio_readl(GPIO_IN(offset))>>  GPIO_BIT(offset))&  0x1;
>>   }
> Any chance of using the same kind of logic to isolate the bit value? One
> branch above does !!(val&  mask) and the other (val>>  shift)&  1.

It was going to more than 80 column and hence I did like this.  Let me 
respin this patch to have same kind of.