linux-kernel - Re: [PATCH v3] Fix IMX PWM period setting

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Message-ID: <vi2hrue6l5g5ihoa3rh2u3pitgbwiyvr5su6dhztg6iowajwfw@6rj6lh5fbtb4>
Date: Mon, 3 Nov 2025 11:19:52 +0100
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: "Krebs, Olaf" <Olaf.Krebs@...-metering.com>
Cc: Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
	Pengutronix Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>, 
	"open list:PWM SUBSYSTEM" <linux-pwm@...r.kernel.org>, 
	"open list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" <imx@...ts.linux.dev>, 
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] Fix IMX PWM period setting

Hello Olaf,

On Mon, Nov 03, 2025 at 06:50:20AM +0000, Krebs, Olaf wrote:
> From: Olaf Krebs <okr@...w.emh-meter.de>
> 
> If a second PWM is requested by a driver before the first is configured, trying to configure any of these results in .user_count > 1 and thus the configuration fails.
> Fix that by only erroring out by additionally checking if the period is actually configured.
> 
> Exapmle: Using of 3 PWM channels to control a RGB LED.
> 
> DTS-Config for an imx93-Board:
> 	...
> 	led-controller {
> 		compatible = "pwm-leds-multicolor";
> 		multi-led {
> 			label = "RGBled";
> 			color = <LED_COLOR_ID_RGB>;
> 			function = LED_FUNCTION_INDICATOR;
> 			max-brightness = <255>;
> 			led-red {
> 				pwms = <&tpm5 0 1000000 PWM_POLARITY_INVERTED>;
> 				color = <LED_COLOR_ID_RED>;
> 			};
> 			led-green {
> 				pwms = <&tpm6 2 1000000 PWM_POLARITY_INVERTED>;
> 				color = <LED_COLOR_ID_GREEN>;
> 			};
> 			led-blue {
> 				pwms = <&tpm5 1 1000000 PWM_POLARITY_INVERTED>;
> 				color = <LED_COLOR_ID_BLUE>;
> 			};
> 		};
> 	};
> 	...
> 
> Without this patch, an BUSY-error message is generated during initialization.
> 
> [    7.395326] leds_pwm_multicolor led-controller: error -EBUSY: failed to set led PWM value for (null)
> [    7.405167] leds_pwm_multicolor led-controller: probe with driver leds_pwm_multicolor failed with error -16
> 
> Signed-off-by: Olaf krebs <olaf.krebs@...-metering.com>

checkpatch is still unhappy with your patch. That might be (at least
partially) the fault of your MUA or MTA.

> ---
>  drivers/pwm/pwm-imx-tpm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-imx-tpm.c b/drivers/pwm/pwm-imx-tpm.c index 5b399de16d60..411daa7711f1 100644
> --- a/drivers/pwm/pwm-imx-tpm.c
> +++ b/drivers/pwm/pwm-imx-tpm.c
> @@ -190,7 +190,7 @@ static int pwm_imx_tpm_apply_hw(struct pwm_chip *chip,
>  		 * there are multiple channels in use with different
>  		 * period settings.
>  		 */
> -		if (tpm->user_count > 1)
> +		if ((tpm->user_count > 1) && (tpm->real_period != 0))
>  			return -EBUSY;

Repeating my review for v2:
> Please drop the added parenthesis.

Have you considered "I wonder if a saner check would involve
enable_count instead of user_count."?

Best regards
Uwe

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