linux-kernel - Re: [PATCH v7]pwm: add BCM2835 PWM driver

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Message-ID: <20141014135445.GA26015@ulmo>
Date:	Tue, 14 Oct 2014 15:54:47 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Bart Tanghe <bart.tanghe@...masmore.be>
Cc:	matt.porter@...aro.org, linux-kernel@...r.kernel.org,
	linux-pwm@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH v7]pwm: add BCM2835 PWM driver

On Wed, Oct 08, 2014 at 12:14:32PM +0200, Bart Tanghe wrote:
[...]
> diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c
[...]
> +static void bcm2835_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct bcm2835_pwm *pc = to_bcm2835_pwm(chip);
> +	u32 value;
> +
> +	value = readl(pc->base);
> +	value &= (~DEFAULT_PWM_MODE << (PWM_CONTROL_STRIDE * pwm->hwpwm));

While applying I noticed this oddity. Is this meant to be:

	value &= ~(DEFAULT_PWM_MODE << (PWM_CONTROL_STRIDE * pwm->hwpwm));

? That would match what's in bcm2835_pwm_request(). If so, what's the
difference between DEFAULT_PWM_MODE and PWM_CONTROL_MASK? Is the value
of a channel's field 0xff or 0x00 in the default mode?

The above indicates that it would be 0x00, in which case it might be
better to just do...

	value &= ~(PWM_CONTROL_MASK << (PWM_CONTROL_STRIDE * pwm->hwpwm));

... and get rid of DEFAULT_PWM_MODE.

No need to respin, I can fix this up when applying. Just let me know if
that's actually the right thing to do.

Thierry

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