Re: [PATCH 3/7] hwmon: (max31790) Fix pwmX_enable attributes

From: "Jan Kundrát" <jan.kundrat@cesnet.cz>
To: Guenter Roeck <linux@roeck-us.net>
Cc: <linux-hwmon@vger.kernel.org>, Jean Delvare <jdelvare@suse.com>,
	<kubernat@cesnet.cz>
Subject: Re: [PATCH 3/7] hwmon: (max31790) Fix pwmX_enable attributes
Date: Wed, 02 Jun 2021 14:44:15 +0200	[thread overview]
Message-ID: <18b3e371-9e37-4887-8c05-161e6a2dcb88@cesnet.cz> (raw)
In-Reply-To: <20210526154022.3223012-4-linux@roeck-us.net>

On středa 26. května 2021 17:40:18 CEST, Guenter Roeck wrote:
> pwmX_enable supports three possible values:
>
> 0: Fan control disabled. Duty cycle is fixed to 0%
> 1: Fan control enabled, pwm mode. Duty cycle is determined by
>    values written into Target Duty Cycle registers.
> 2: Fan control enabled, rpm mode
>    Duty cycle is adjusted such that fan speed matches
>    the values in Target Count registers
>
> The current code does not do this; instead, it mixes pwm control
> configuration with fan speed monitoring configuration. Worse, it
> reports that pwm control would be disabled (pwmX_enable==0) when
> it is in fact enabled in pwm mode. Part of the problem may be that
> the chip sets the "TACH input enable" bit on its own whenever the
> mode bit is set to RPM mode, but that doesn't mean that "TACH input
> enable" accurately reflects the pwm mode.
>
> Fix it up and only handle pwm control with the pwmX_enable attributes.
> In the documentation, clarify that disabling pwm control (pwmX_enable=0)
> sets the pwm duty cycle to 0%. In the code, explain why TACH_INPUT_EN
> is set together with RPM_MODE.
>
> While at it, only update the configuration register if the configuration
> has changed, and only update the cached configuration if updating the
> chip configuration was successful.
>
> Cc: Jan Kundrát <jan.kundrat@cesnet.cz>
> Cc: Václav Kubernát <kubernat@cesnet.cz>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Reviewed-by: Jan Kundrát <jan.kundrat@cesnet.cz>

Cheers,
Jan