linux-kernel - Re: [PATCH] pwm-imx: Fix config / enable / disable

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Date:	Tue, 28 Aug 2012 09:37:44 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Benoît Thébaudeau 
	<benoit.thebaudeau@...ansee.com>
Cc:	Thierry Reding <thierry.reding@...onic-design.de>,
	linux-kernel@...r.kernel.org, Sascha Hauer <kernel@...gutronix.de>,
	linux-arm-kernel@...ts.infradead.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, Bryan Wu <bryan.wu@...onical.com>,
	Richard Purdie <rpurdie@...ys.net>, linux-leds@...r.kernel.org,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	linux-fbdev@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH] pwm-imx: Fix config / enable / disable

On Thu, Aug 23, 2012 at 11:03:57PM +0200, Benoît Thébaudeau wrote:
> imx_pwm_config() did not enable the PWM IP clock while accessing the registers.
> Hence, a call to pwm_config() had no effect before pwm_enable() had been called,
> which does not comply to the PWM API.
> 
> Moreover, calling pwm_disable() then pwm_enable() must be a transparent
> operation.
> 
> This fixes the first setting of brightness through sysfs that had no effect with
> leds-pwm.

I don't really like this patch. I'd like to have this one first, it
makes further cleanups easier:

https://lkml.org/lkml/2012/8/28/24

Simililarly, we should probably introduce a imx_pwm_[en|dis]able_v[12]

Then, the pwm core already makes sure that pwm_enable/disable are called
only once, so the if (imx->clk_enabled) in pwm_enable/disable is
unnecessary.

Sascha

> 
> Cc: Thierry Reding <thierry.reding@...onic-design.de>
> Cc: <linux-kernel@...r.kernel.org>
> Cc: Sascha Hauer <kernel@...gutronix.de>
> Cc: <linux-arm-kernel@...ts.infradead.org>
> Cc: Benoît Thébaudeau <benoit.thebaudeau@...ansee.com>
> Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@...ansee.com>
> ---
>  .../drivers/pwm/pwm-imx.c                          |   55 +++++++++++++++-----
>  1 file changed, 43 insertions(+), 12 deletions(-)
> 
> diff --git linux-next-c94456b.orig/drivers/pwm/pwm-imx.c linux-next-c94456b/drivers/pwm/pwm-imx.c
> index 2a0b353..0519bf2 100644
> --- linux-next-c94456b.orig/drivers/pwm/pwm-imx.c
> +++ linux-next-c94456b/drivers/pwm/pwm-imx.c
> @@ -55,6 +55,16 @@ static int imx_pwm_config(struct pwm_chip *chip,
>  {
>  	struct imx_chip *imx = to_imx_chip(chip);
>  
> +	/*
> +	 * If the PWM is disabled, make sure to turn on the clock before
> +	 * accessing the registers.
> +	 */
> +	if (!imx->clk_enabled) {
> +		int rc = clk_prepare_enable(imx->clk);
> +		if (rc)
> +			return rc;
> +	}
> +
>  	if (!(cpu_is_mx1() || cpu_is_mx21())) {
>  		unsigned long long c;
>  		unsigned long period_cycles, duty_cycles, prescale;
> @@ -85,8 +95,11 @@ static int imx_pwm_config(struct pwm_chip *chip,
>  		writel(period_cycles, imx->mmio_base + MX3_PWMPR);
>  
>  		cr = MX3_PWMCR_PRESCALER(prescale) |
> -			MX3_PWMCR_DOZEEN | MX3_PWMCR_WAITEN |
> -			MX3_PWMCR_DBGEN | MX3_PWMCR_EN;
> +			MX3_PWMCR_DOZEEN | MX3_PWMCR_WAITEN | MX3_PWMCR_DBGEN;
> +
> +		/* If the PWM is enabled, keep it so. */
> +		if (imx->clk_enabled)
> +			cr |= MX3_PWMCR_EN;
>  
>  		if (cpu_is_mx25())
>  			cr |= MX3_PWMCR_CLKSRC_IPG;
> @@ -118,32 +131,50 @@ static int imx_pwm_config(struct pwm_chip *chip,
>  		BUG();
>  	}
>  
> +	/* If the PWM is disabled, turn the clock off again to save power. */
> +	if (!imx->clk_enabled)
> +		clk_disable_unprepare(imx->clk);
> +
>  	return 0;
>  }
>  
>  static int imx_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
>  {
>  	struct imx_chip *imx = to_imx_chip(chip);
> -	int rc = 0;
> +	int rc;
>  
> -	if (!imx->clk_enabled) {
> -		rc = clk_prepare_enable(imx->clk);
> -		if (!rc)
> -			imx->clk_enabled = 1;
> +	if (imx->clk_enabled)
> +		return 0;
> +
> +	rc = clk_prepare_enable(imx->clk);
> +	if (rc)
> +		return rc;
> +
> +	if (!(cpu_is_mx1() || cpu_is_mx21())) {
> +		u32 cr = readl(imx->mmio_base + MX3_PWMCR);
> +		cr |= MX3_PWMCR_EN;
> +		writel(cr, imx->mmio_base + MX3_PWMCR);
>  	}
> -	return rc;
> +
> +	imx->clk_enabled = 1;
> +	return 0;
>  }
>  
>  static void imx_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>  {
>  	struct imx_chip *imx = to_imx_chip(chip);
>  
> -	writel(0, imx->mmio_base + MX3_PWMCR);
> +	if (!imx->clk_enabled)
> +		return;
>  
> -	if (imx->clk_enabled) {
> -		clk_disable_unprepare(imx->clk);
> -		imx->clk_enabled = 0;
> +	if (!(cpu_is_mx1() || cpu_is_mx21())) {
> +		u32 cr = readl(imx->mmio_base + MX3_PWMCR);
> +		cr &= ~MX3_PWMCR_EN;
> +		writel(cr, imx->mmio_base + MX3_PWMCR);
>  	}
> +
> +	clk_disable_unprepare(imx->clk);
> +	imx->clk_enabled = 0;
>  }
>  
>  static struct pwm_ops imx_pwm_ops = {
> --
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