linux-kernel - Re: [PATCH] gpio: tegra: read output value when gpio is set in direction

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Date:	Fri, 9 Nov 2012 11:17:57 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	Stephen Warren <swarren@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] gpio: tegra: read output value when gpio is set in direction_out

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.
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