linux-kernel - Re: [REGRESSION] hwmon: (applesmc) avoid overlong udelay()

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Message-ID: <20200930164446.GB219887@roeck-us.net>
Date:   Wed, 30 Sep 2020 09:44:46 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     rydberg@...math.org, jdelvare@...e.com,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [REGRESSION] hwmon: (applesmc) avoid overlong udelay()

On Wed, Sep 30, 2020 at 10:54:42AM +0200, Andreas Kemnade wrote:
> Hi,
> 
> after the $subject patch I get lots of errors like this:

For reference, this refers to commit fff2d0f701e6 ("hwmon: (applesmc)
avoid overlong udelay()").

> [  120.378614] applesmc: send_byte(0x00, 0x0300) fail: 0x40
> [  120.378621] applesmc: LKSB: write data fail
> [  120.512782] applesmc: send_byte(0x00, 0x0300) fail: 0x40
> [  120.512787] applesmc: LKSB: write data fail
> 
> CPU sticks at low speed and no fan is turning on.
> Reverting this patch on top of 5.9-rc6 solves this problem.
> 
> Some information from dmidecode:
> 
> Base Board Information
>         Manufacturer: Apple Inc.
>         Product Name: Mac-7DF21CB3ED6977E5
>         Version: MacBookAir6,2
>  
> Handle 0x0020, DMI type 11, 5 bytes OEM Strings         String 1: Apple ROM Version.  Model:       …, 
> Handle 0x0020, DMI type 11, 5 bytes
> OEM Strings
>         String 1: Apple ROM Version.  Model:        MBA61.  EFI Version:  122.0.0
>         String 2: .0.0.  Built by:     root@...mon.  Date:         Wed Jun 10 18:
>         String 3: 10:36 PDT 2020.  Revision:     122 (B&I).  ROM Version:  F000_B
>         String 4: 00.  Build Type:   Official Build, Release.  Compiler:     Appl
>         String 5: e clang version 3.0 (tags/Apple/clang-211.10.1) (based on LLVM
>         String 6: 3.0svn).
>  
> Writing to things in /sys/devices/platform/applesmc.768 gives also the
> said errors.
> But writing 1 to fan1_maunal and 5000 to fan1_output turns the fan on
> despite error messages.
> 
Not really sure what to do here. I could revert the patch, but then we'd gain
clang compile failures. Arnd, any idea ?

Guenter