linux-kernel - Re: [PATCH 1/6] pwm: imx: Rewrite imx_pwm_*_v1 code to facilitate switch to atomic pwm operation

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Date:   Tue, 25 Oct 2016 07:54:54 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Lukasz Majewski <l.majewski@...ess.pl>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Stefan Agner <stefan@...er.ch>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        linux-pwm@...r.kernel.org,
        Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de,
        Fabio Estevam <fabio.estevam@....com>,
        Fabio Estevam <festevam@...il.com>,
        Lothar Wassmann <LW@...o-electronics.de>
Subject: Re: [PATCH 1/6] pwm: imx: Rewrite imx_pwm_*_v1 code to facilitate
 switch to atomic pwm operation

On Sun, Oct 23, 2016 at 11:45:41PM +0200, Lukasz Majewski wrote:
> The code has been rewritten to remove "generic" calls to
> imx_pwm_{enable|disable|config}.
> 
> Such approach would facilitate switch to atomic PWM (a.k.a ->apply())
> implementation.
> 
> Suggested-by: Stefan Agner <stefan@...er.ch>
> Suggested-by: Boris Brezillon <boris.brezillon@...e-electrons.com>
> Signed-off-by: Lukasz Majewski <l.majewski@...ess.pl>
> ---
>  drivers/pwm/pwm-imx.c | 46 ++++++++++++++++++++++++++++++++++------------
>  1 file changed, 34 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
> index c37d223..83e43d5 100644
> --- a/drivers/pwm/pwm-imx.c
> +++ b/drivers/pwm/pwm-imx.c
> @@ -66,8 +66,6 @@ struct imx_chip {
>  static int imx_pwm_config_v1(struct pwm_chip *chip,
>  		struct pwm_device *pwm, int duty_ns, int period_ns)
>  {
> -	struct imx_chip *imx = to_imx_chip(chip);
> -
>  	/*
>  	 * The PWM subsystem allows for exact frequencies. However,
>  	 * I cannot connect a scope on my device to the PWM line and
> @@ -85,26 +83,52 @@ static int imx_pwm_config_v1(struct pwm_chip *chip,
>  	 * both the prescaler (/1 .. /128) and then by CLKSEL
>  	 * (/2 .. /16).
>  	 */
> +	struct imx_chip *imx = to_imx_chip(chip);
>  	u32 max = readl(imx->mmio_base + MX1_PWMP);
>  	u32 p = max * duty_ns / period_ns;
> +	int ret;
> +
> +	ret = clk_prepare_enable(imx->clk_ipg);
> +	if (ret)
> +		return ret;
> +
>  	writel(max - p, imx->mmio_base + MX1_PWMS);
>  
> +	clk_disable_unprepare(imx->clk_ipg);
> +
>  	return 0;
>  }
>  
> -static void imx_pwm_set_enable_v1(struct pwm_chip *chip, bool enable)
> +static int imx_pwm_enable_v1(struct pwm_chip *chip, struct pwm_device *pwm)
>  {
>  	struct imx_chip *imx = to_imx_chip(chip);
> +	int ret;
>  	u32 val;
>  
> +	ret = clk_prepare_enable(imx->clk_ipg);
> +	if (ret)
> +		return ret;
> +
>  	val = readl(imx->mmio_base + MX1_PWMC);
> +	val |= MX1_PWMC_EN;
> +	writel(val, imx->mmio_base + MX1_PWMC);
>  
> -	if (enable)
> -		val |= MX1_PWMC_EN;
> -	else
> -		val &= ~MX1_PWMC_EN;
> +	clk_disable_unprepare(imx->clk_per);

This looks wrong. You start by enabling clk_ipg which is needed for
register access, but then end with disabling clk_per which is needed for
driving the actual PWM output. This function should probably enable
clk_per on entry and enable clk_ipg while accessing registers.

Sascha

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