linux-kernel - Re: [PATCH 05/14] pwm: rockchip: Avoid glitches on already running PWMs

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Message-ID: <20160603202859.GD124478@google.com>
Date:	Fri, 3 Jun 2016 13:28:59 -0700
From:	Brian Norris <briannorris@...omium.org>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	linux-pwm@...r.kernel.org, Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	linux-rockchip@...ts.infradead.org,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Milo Kim <milo.kim@...com>,
	Doug Anderson <dianders@...gle.com>,
	Caesar Wang <wxt@...k-chips.com>,
	Stephen Barber <smbarber@...omium.org>,
	Ajit Pal Singh <ajitpal.singh@...com>,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
	Maxime Coquelin <maxime.coquelin@...com>,
	Patrice Chotard <patrice.chotard@...com>, kernel@...inux.com
Subject: Re: [PATCH 05/14] pwm: rockchip: Avoid glitches on already running
 PWMs

Hi,

Just noticed a few things:

On Fri, Jun 03, 2016 at 10:23:03AM +0200, Boris Brezillon wrote:
> The current logic will disable the PWM clk even if the PWM was left
> enabled by the bootloader (because it's controlling a critical device
> like a regulator for example).
> Keep the PWM clk enabled if the PWM is enabled to avoid any glitches.
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> ---
>  drivers/pwm/pwm-rockchip.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-rockchip.c b/drivers/pwm/pwm-rockchip.c
> index dfacf7d..798a787 100644
> --- a/drivers/pwm/pwm-rockchip.c
> +++ b/drivers/pwm/pwm-rockchip.c
> @@ -299,6 +299,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev)
>  {
>  	const struct of_device_id *id;
>  	struct rockchip_pwm_chip *pc;
> +	struct pwm_state state;
>  	struct resource *r;
>  	int ret;
>  
> @@ -319,7 +320,7 @@ static int rockchip_pwm_probe(struct platform_device *pdev)
>  	if (IS_ERR(pc->clk))
>  		return PTR_ERR(pc->clk);
>  
> -	ret = clk_prepare(pc->clk);
> +	ret = clk_prepare_enable(pc->clk);
>  	if (ret)
>  		return ret;
>  
> @@ -342,12 +343,33 @@ static int rockchip_pwm_probe(struct platform_device *pdev)
>  		dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
>  	}
>  
> +	/* Keep the PWM clk enabled if the PWM appears to be up and running. */
> +	pwm_get_state(pc->chip.pwms, &state);
> +	if (!state.enabled)

Why not just if (!pwm_is_enabled())?

> +		clk_disable(pc->clk);
> +
>  	return ret;
>  }
>  
>  static int rockchip_pwm_remove(struct platform_device *pdev)
>  {
>  	struct rockchip_pwm_chip *pc = platform_get_drvdata(pdev);
> +	struct pwm_state state;
> +
> +	/*
> +	 * Disable the PWM clk before unpreparing it if the PWM device is still
> +	 * running. This should only happen when the last PWM user left it
> +	 * enabled, or when nobody requested a PWM that was previously enabled
> +	 * by the bootloader.
> +	 *
> +	 * FIXME: Maybe the core should disable all PWM devices in
> +	 * pwmchip_remove(). In this case we'd only have to call
> +	 * clk_unprepare() after pwmchip_remove().
> +	 *
> +	 */
> +	pwm_get_state(pc->chip.pwms, &state);
> +	if (state.enabled)

Same here.

With that:

Reviewed-by: Brian Norris <briannorris@...omium.org>

And it tests out fine:

Tested-by: Brian Norris <briannorris@...omium.org>


> +		clk_disable(pc->clk);
>  
>  	clk_unprepare(pc->clk);
>  
> -- 
> 2.7.4
>