linux-kernel - Re: [PATCH] pwm: imx-tpm: keep channel state instead of counting

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Message-ID: <sqpcohdky6m2kz5o7izoclr7k4wi2s72mi4ojrdhr2kbogtfbt@v6y5raizg2n5>
Date: Sat, 31 Jan 2026 00:00:02 +0100
From: Uwe Kleine-König <ukleinek@...nel.org>
To: "Viorel Suman (OSS)" <viorel.suman@....nxp.com>
Cc: Frank Li <Frank.Li@....com>, Sascha Hauer <s.hauer@...gutronix.de>, 
	Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>, linux-pwm@...r.kernel.org, 
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pwm: imx-tpm: keep channel state instead of counting

Hello,

On Fri, Jan 30, 2026 at 04:37:20PM +0200, Viorel Suman (OSS) wrote:
> diff --git a/drivers/pwm/pwm-imx-tpm.c b/drivers/pwm/pwm-imx-tpm.c
> index 5b399de16d60..0f8643f4a70b 100644
> --- a/drivers/pwm/pwm-imx-tpm.c
> +++ b/drivers/pwm/pwm-imx-tpm.c
> @@ -62,7 +62,7 @@ struct imx_tpm_pwm_chip {
>  	void __iomem *base;
>  	struct mutex lock;
>  	u32 user_count;
> -	u32 enable_count;
> +	u32 enabled_channels;
>  	u32 real_period;
>  };
>  
> @@ -166,6 +166,10 @@ static int pwm_imx_tpm_get_state(struct pwm_chip *chip,
>  
>  	/* get channel status */
>  	state->enabled = FIELD_GET(PWM_IMX_TPM_CnSC_ELS, val) ? true : false;
> +	if (state->enabled)
> +		tpm->enabled_channels |= BIT(pwm->hwpwm);
> +	else
> +		tpm->enabled_channels &= ~BIT(pwm->hwpwm);

I'm not sure about this being the right approach, feels like the driver
sells the pwm core down the river resulting in something the might work
now but isn't robust.

If I understand it right, keeping the enable count balanced depends on
.get_state() being called.

The usual and robust approach is that .probe() checks the device state
and initializes enable counts and the like accordingly.
 
>  	return 0;
>  }
> @@ -282,15 +286,19 @@ static int pwm_imx_tpm_apply_hw(struct pwm_chip *chip,
>  	}
>  	writel(val, tpm->base + PWM_IMX_TPM_CnSC(pwm->hwpwm));
>  
> -	/* control the counter status */
> +	/* control the channel state */
>  	if (state->enabled != c.enabled) {
>  		val = readl(tpm->base + PWM_IMX_TPM_SC);
>  		if (state->enabled) {
> -			if (++tpm->enable_count == 1)
> +			if (tpm->enabled_channels == 0) {
>  				val |= PWM_IMX_TPM_SC_CMOD_INC_EVERY_CLK;
> +			}

No { } for one line blocks please.

> +			tpm->enabled_channels |= BIT(pwm->hwpwm);
>  		} else {
> -			if (--tpm->enable_count == 0)
> +			tpm->enabled_channels &= ~BIT(pwm->hwpwm);
> +			if (tpm->enabled_channels == 0) {
>  				val &= ~PWM_IMX_TPM_SC_CMOD;
> +			}
>  		}
>  		writel(val, tpm->base + PWM_IMX_TPM_SC);
>  	}

Best regards
Uwe

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