linux-kernel - Re: [PATCH v4] pwm: atmel: Enable clk when pwm already enabled in bootloader

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Message-ID: <20230712135553.trqkxtcuiemwzgwe@pengutronix.de>
Date:   Wed, 12 Jul 2023 15:55:53 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Guiting Shen <aarongt.shen@...il.com>
Cc:     thierry.reding@...il.com, claudiu.beznea@...rochip.com,
        nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
        linux-arm-kernel@...ts.infradead.org, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] pwm: atmel: Enable clk when pwm already enabled in
 bootloader

On Wed, Jul 12, 2023 at 09:43:47PM +0800, Guiting Shen wrote:
> The driver would never call clk_enable() if the PWM channel was already
> enabled in bootloader which lead to dump the warning message "the PWM
> clock already disabled" when turning off the PWM channel.
> 
> Add atmel_pwm_enable_clk_if_on() in probe function to enable clock if
> the PWM channel was already enabled in bootloader.
> 
> Signed-off-by: Guiting Shen <aarongt.shen@...il.com>
> ---
>  drivers/pwm/pwm-atmel.c | 40 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index cdbc23649032..28ea0f7267ca 100644
> --- a/drivers/pwm/pwm-atmel.c
> +++ b/drivers/pwm/pwm-atmel.c
> @@ -36,7 +36,7 @@
>  #define PWM_SR			0x0C
>  #define PWM_ISR			0x1C
>  /* Bit field in SR */
> -#define PWM_SR_ALL_CH_ON	0x0F
> +#define PWM_SR_ALL_CH_MASK	0x0F
>  
>  /* The following register is PWM channel related registers */
>  #define PWM_CH_REG_OFFSET	0x200
> @@ -464,6 +464,37 @@ static const struct of_device_id atmel_pwm_dt_ids[] = {
>  };
>  MODULE_DEVICE_TABLE(of, atmel_pwm_dt_ids);
>  
> +static int atmel_pwm_enable_clk_if_on(struct atmel_pwm_chip *atmel_pwm)
> +{
> +	unsigned int i;
> +	int err;
> +	u32 sr;
> +
> +	sr = atmel_pwm_readl(atmel_pwm, PWM_SR);
> +	if (!(sr & PWM_SR_ALL_CH_MASK))
> +		return 0;
> +
> +	for (i = 0; i < atmel_pwm->chip.npwm; i++) {
> +		if (!(sr & (1 << i)))
> +			continue;
> +
> +		err = clk_enable(atmel_pwm->clk);
> +		if (err) {
> +			dev_err(atmel_pwm->chip.dev,
> +				"failed to enable clock for pwm #%d: %pe\n",
> +							i, ERR_PTR(err));
> +
> +			while (i--) {
> +				if (sr & (1 << i))
> +					clk_disable(atmel_pwm->clk);
> +			}
> +			return err;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  static int atmel_pwm_probe(struct platform_device *pdev)
>  {
>  	struct atmel_pwm_chip *atmel_pwm;
> @@ -504,8 +535,15 @@ static int atmel_pwm_probe(struct platform_device *pdev)
>  
>  	platform_set_drvdata(pdev, atmel_pwm);
>  
> +	ret = atmel_pwm_enable_clk_if_on(atmel_pwm);
> +	if (ret < 0)
> +		goto remove_pwmchip;
> +
>  	return ret;
>  
> +remove_pwmchip:
> +	pwmchip_remove(&atmel_pwm->chip);
> +

I'd consider it more natural to do the atmel_pwm_enable_clk_if_on() call
before registering the pwmchip. But I guess it works like this, too.
(Well unless it's possible that there are set bits in PWM_SR and the
clock is off.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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