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

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Message-ID: <20211130103854.gwt5bib34t2qvbgg@pengutronix.de>
Date:   Tue, 30 Nov 2021 11:38:54 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Billy Tsai <billy_tsai@...eedtech.com>
Cc:     b.zolnierkie@...sung.com, jdelvare@...e.com, linux@...ck-us.net,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        BMC-SW@...eedtech.com, stable@...r.kernel.org
Subject: Re: [PATCH] hwmon: (pwm-fan) Ensure the fan going on in .probe()

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@...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>

Nice commit log :-)

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

Best regards
Uwe

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

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