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Subject: Re: [PATCH v5 1/1] applesmc: Re-work SMC comms
To:     Brad Campbell <brad@fnarfbargle.com>, linux-hwmon@vger.kernel.org
Cc:     Arnd Bergmann <arnd@arndb.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        hns@goldelico.com, Andreas Kemnade <andreas@kemnade.info>,
        Jean Delvare <jdelvare@suse.com>,
        Guenter Roeck <linux@roeck-us.net>
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From:   Henrik Rydberg <rydberg@bitmath.org>
Message-ID: <29b03865-f00a-f121-b7a5-c4b9179a27cb@bitmath.org>
Date:   Wed, 11 Nov 2020 21:05:59 +0100
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On 2020-11-11 14:06, Brad Campbell wrote:
> Commit fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
> introduced an issue whereby communication with the SMC became
> unreliable with write errors like :
> 
> [  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
> 
> The original code appeared to be timing sensitive and was not reliable
> with the timing changes in the aforementioned commit.
> 
> This patch re-factors the SMC communication to remove the timing
> dependencies and restore function with the changes previously
> committed. Logic changes based on inspection of the Apple SMC kext.
> 
> Tested on : MacbookAir6,2 MacBookPro11,1 iMac12,2, MacBookAir1,1,
> MacBookAir3,1
> 
> Fixes: fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
> Reported-by: Andreas Kemnade <andreas@kemnade.info>
> Tested-by: Andreas Kemnade <andreas@kemnade.info> # MacBookAir6,2
> Acked-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Brad Campbell <brad@fnarfbargle.com>
> Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
> 
> ---
> Changelog :
> v1 : Initial attempt
> v2 : Address logic and coding style
> v3 : Removed some debug hangover. Added tested-by. Modifications for MacBookAir1,1
> v4 : Re-factored logic based on Apple driver. Simplified wait_status loop
> v5 : Re-wrote status loop. Simplified busy check in send_byte(). Fixed formatting

Hi Brad,

This version is still working fine on the MBA1,1, at 50 reads per second.

Thanks,
Henrik