linux-kernel - Re: [PATCH] Add Second Fan Support for Thinkpad P50

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Message-ID: <5490267.oBufKZg01J@lenovodario>
Date:   Sat, 20 Jul 2019 17:22:00 +0200
From:   Dario Messina <nanodario@...il.com>
To:     Stefan Assmann <sassmann@...nic.de>
Cc:     Alexander Kappner <agk@...king.net>, ibm-acpi@....eng.br,
        dvhart@...radead.org, andy@...radead.org,
        ibm-acpi-devel@...ts.sourceforge.net,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add Second Fan Support for Thinkpad P50

I have a Thinkpad P51 (BIOS version: N1UET74W, EC version: N1UHT26W).
This patch works on my computer and I can read both fan speeds through sysfs 
interface.

On 2018-09-26 16:34:19 CEST, Stefan Assmann wrote:
> Is there a way to actually control the second fan? There's pwm1, but no
> pwm2. And pwm1 only affects fan1.

I have played with the driver code and I noticed that it is possible to 
control both fans independently (unlike what the "Fan subdriver" comment in 
the code says).
You can do that simply by calling fan_select_fan1 or fan_select_fan2, to 
select a fan to be controlled, before calling fan_set_level. All control 
parameters (disengaged, manual speeds, auto) are fully independent.

What is not smooth is reading back current control parameters from register 
0x2f (like fan_pwm1_show or fan_pwm1_enable_show actually do), because the EC 
ignores which fan is currently selected and it always returns the last written 
value.

Distinti Saluti/Best Regards,
Dario Messina