[PATCH] hwmon: (pwm-fan) Ensure the fan going on in .probe()

[PATCH] hwmon: (pwm-fan) Ensure the fan going on in .probe()

[Billy Tsai]

Before commit 86585c61972f ("hwmon: (pwm-fan) stop using legacy
PWM functions and some cleanups") pwm_apply_state() was called
unconditionally in pwm_fan_probe(). In this commit this direct
call was replaced by a call to __set_pwm(ct, MAX_PWM) which
however is a noop if ctx->pwm_value already matches the value to
set.
After probe the fan is supposed to run at full speed, and the
internal driver state suggests it does, but this isn't asserted
and depending on bootloader and pwm low-level driver, the fan
might just be off.
So drop setting pwm_value to MAX_PWM to ensure the check in
__set_pwm doesn't make it exit early and the fan goes on as
intended.

Cc: stable@vger.kernel.org
Fixes: 86585c61972f ("hwmon: (pwm-fan) stop using legacy PWM functions and some cleanups")
Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
---
 drivers/hwmon/pwm-fan.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
index 17518b4cab1b..f12b9a28a232 100644
--- a/drivers/hwmon/pwm-fan.c
+++ b/drivers/hwmon/pwm-fan.c
@@ -336,8 +336,6 @@ static int pwm_fan_probe(struct platform_device *pdev)
 			return ret;
 	}
 
-	ctx->pwm_value = MAX_PWM;
-
 	pwm_init_state(ctx->pwm, &ctx->pwm_state);
 
 	/*
-- 
2.25.1

Re: [PATCH] hwmon: (pwm-fan) Ensure the fan going on in .probe()

[Uwe Kleine-König]

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On Tue, Nov 30, 2021 at 05:22:12PM +0800, Billy Tsai wrote:
> Before commit 86585c61972f ("hwmon: (pwm-fan) stop using legacy
> PWM functions and some cleanups") pwm_apply_state() was called
> unconditionally in pwm_fan_probe(). In this commit this direct
> call was replaced by a call to __set_pwm(ct, MAX_PWM) which
> however is a noop if ctx->pwm_value already matches the value to
> set.
> After probe the fan is supposed to run at full speed, and the
> internal driver state suggests it does, but this isn't asserted
> and depending on bootloader and pwm low-level driver, the fan
> might just be off.
> So drop setting pwm_value to MAX_PWM to ensure the check in
> __set_pwm doesn't make it exit early and the fan goes on as
> intended.
> 
> Cc: stable@vger.kernel.org
> Fixes: 86585c61972f ("hwmon: (pwm-fan) stop using legacy PWM functions and some cleanups")
> Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>

Nice commit log :-)

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Best regards
Uwe

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

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Re: [PATCH] hwmon: (pwm-fan) Ensure the fan going on in .probe()

[Guenter Roeck]

On 11/30/21 1:22 AM, Billy Tsai wrote:
> Before commit 86585c61972f ("hwmon: (pwm-fan) stop using legacy
> PWM functions and some cleanups") pwm_apply_state() was called
> unconditionally in pwm_fan_probe(). In this commit this direct
> call was replaced by a call to __set_pwm(ct, MAX_PWM) which
> however is a noop if ctx->pwm_value already matches the value to
> set.
> After probe the fan is supposed to run at full speed, and the
> internal driver state suggests it does, but this isn't asserted
> and depending on bootloader and pwm low-level driver, the fan
> might just be off.
> So drop setting pwm_value to MAX_PWM to ensure the check in
> __set_pwm doesn't make it exit early and the fan goes on as
> intended.
> 
> Cc: stable@vger.kernel.org
> Fixes: 86585c61972f ("hwmon: (pwm-fan) stop using legacy PWM functions and some cleanups")
> Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>

I'll apply this patch, but _please_ version your patches in the future
and provide a change log.

Guenter

> ---
>   drivers/hwmon/pwm-fan.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 17518b4cab1b..f12b9a28a232 100644
> --- a/drivers/hwmon/pwm-fan.c
> +++ b/drivers/hwmon/pwm-fan.c
> @@ -336,8 +336,6 @@ static int pwm_fan_probe(struct platform_device *pdev)
>   			return ret;
>   	}
>   
> -	ctx->pwm_value = MAX_PWM;
> -
>   	pwm_init_state(ctx->pwm, &ctx->pwm_state);
>   
>   	/*
>