linux-kernel - RE: [PWM PATCH 2/5] Emulates PWM hardware using a high-resolution timer and a GPIO pin

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Message-ID: <BD79186B4FD85F4B8E60E381CAEE190902153515@mi8nycmail19.Mi8.com>
Date:	Fri, 12 Feb 2010 08:53:30 -0500
From:	"H Hartley Sweeten" <hartleys@...ionengravers.com>
To:	"Bill Gatliff" <bgat@...lgatliff.com>,
	"Pavel Machek" <pavel@....cz>
Cc:	<linux-embedded@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PWM PATCH 2/5] Emulates PWM hardware using a high-resolution timer and a GPIO pin

Thursday, February 11, 2010 1:35 PM, Bill Gatliff wrote:
> Pavel Machek wrote:
>>> +static void
>>> +gpio_pwm_work (struct work_struct *work)
>>> +{
>>> +	struct gpio_pwm *gp = container_of(work, struct gpio_pwm, work);
>>> +
>>> +	if (gp->active)
>>> +		gpio_direction_output(gp->gpio, gp->polarity ? 1 : 0);
>>> +	else
>>> +		gpio_direction_output(gp->gpio, gp->polarity ? 0 : 1);
>>> +}
>>>     
>>
>> ...polarity ^ active ?
>>   
>
> ... except that if polarity and/or active are >1, I don't send the
> values 1 or 0 to gpio_direction_output.  I don't know if the API is
> specifically intended to accept nonzero values that are greater than 1.

FWIW, the gpiolib API will accept any non-zero value to "set" a gpio pin
and a zero value to "clear" the pin.

For that matter, some of the gpiolib drivers end up returning the bit
position mask for a given gpio pin and not 1 or 0.  For instance if the
gpio pin in question is bit 6 in an 8-bit register and it is set, a
__gpio_get_value will end up returning 0x40 and not '1'.

Regards,
Hartley
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