linux-kernel - Re: [PATCH v5] pwm: atmel: Enable clk when pwm already enabled in bootloader

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Date:   Sat, 15 Jul 2023 14:12:53 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Guiting Shen <aarongt.shen@...il.com>
Cc:     claudiu.beznea@...rochip.com, thierry.reding@...il.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 v5] pwm: atmel: Enable clk when pwm already enabled in
 bootloader

On Sat, Jul 15, 2023 at 10:36:53AM +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 | 50 +++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 48 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
> index cdbc23649032..4dd6e1319343 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 +464,45 @@ 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, bool on)
> +{
> +	unsigned int i, cnt = 0;
> +	int ret = 0;
> +	u32 sr;
> +
> +	sr = atmel_pwm_readl(atmel_pwm, PWM_SR) & PWM_SR_ALL_CH_MASK;
> +	if (!sr)
> +		return 0;
> +
> +	for (i = 0; i < atmel_pwm->chip.npwm; i++) {
> +		if (sr & (1 << i))
> +			cnt++;
> +	}

If it's just about counting the set bits, there is the function
bitmap_weight().

> +	if (!on)
> +		goto disable_clk;
> +
> +	for (i = 0; i < cnt; i++) {
> +		ret = clk_enable(atmel_pwm->clk);
> +		if (ret) {
> +			dev_err(atmel_pwm->chip.dev,
> +				"failed to enable clock for pwm #%d: %pe\n",
> +							i, ERR_PTR(ret));

The output is bogus here. If SR is say 0xc, and the second enable
fails, it's about pwm #3, but then i is 1.

> +			cnt = i;
> +			goto disable_clk;
> +		}
> +	}
> +
> +	return 0;
> +
> +disable_clk:
> +	while (cnt--)
> +		clk_disable(atmel_pwm->clk);
> +
> +	return ret;
> +}
> +
>  static int atmel_pwm_probe(struct platform_device *pdev)
>  {
>  	struct atmel_pwm_chip *atmel_pwm;

Best regards
Uwe

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

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