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

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Date:   Tue, 30 Nov 2021 06:33:59 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Billy Tsai <billy_tsai@...eedtech.com>, b.zolnierkie@...sung.com,
        jdelvare@...e.com, u.kleine-koenig@...gutronix.de,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     BMC-SW@...eedtech.com, stable@...r.kernel.org
Subject: Re: [PATCH] hwmon: (pwm-fan) Ensure the fan going on in .probe()

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@...r.kernel.org
> Fixes: 86585c61972f ("hwmon: (pwm-fan) stop using legacy PWM functions and some cleanups")
> Signed-off-by: Billy Tsai <billy_tsai@...eedtech.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);
>   
>   	/*
>