linux-kernel - Re: [PATCH v3] applesmc: Re-work SMC comms

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Date:   Mon, 9 Nov 2020 09:44:24 +0100
From:   Andreas Kemnade <andreas@...nade.info>
To:     Henrik Rydberg <rydberg@...math.org>
Cc:     Brad Campbell <brad@...rfbargle.com>,
        Arnd Bergmann <arnd@...db.de>, linux-hwmon@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        hns@...delico.com, Guenter Roeck <linux@...ck-us.net>,
        Jean Delvare <jdelvare@...e.com>
Subject: Re: [PATCH v3] applesmc: Re-work SMC comms

On Sun, 8 Nov 2020 11:14:29 +0100
Henrik Rydberg <rydberg@...math.org> wrote:

> On Sun, Nov 08, 2020 at 09:35:28AM +0100, Henrik Rydberg wrote:
> > Hi Brad,
> > 
> > On 2020-11-08 02:00, Brad Campbell wrote:  
> > > G'day Henrik,
> > > 
> > > I noticed you'd also loosened up the requirement for SMC_STATUS_BUSY in read_smc(). I assume
> > > that causes problems on the early Macbook. This is revised on the one sent earlier.
> > > If you could test this on your Air1,1 it'd be appreciated.  
> > 
> > No, I managed to screw up the patch; you can see that I carefully added the
> > same treatment for the read argument, being unsure if the BUSY state would
> > remain during the AVAILABLE data phase. I can check that again, but
> > unfortunately the patch in this email shows the same problem.
> > 
> > I think it may be worthwhile to rethink the behavior of wait_status() here.
> > If one machine shows no change after a certain status bit change, then
> > perhaps the others share that behavior, and we are waiting in vain. Just
> > imagine how many years of cpu that is, combined. ;-)  
> 
> Here is a modification along that line.
> 
> Compared to your latest version, this one has wait_status() return the
> actual status on success. Instead of waiting for BUSY, it waits for
> the other status bits, and checks BUSY afterwards. So as not to wait
> unneccesarily, the udelay() is placed together with the single
> outb(). The return value of send_byte_data() is augmented with
> -EAGAIN, which is then used in send_command() to create the resend
> loop.
> 
> I reach 41 reads per second on the MBA1,1 with this version, which is
> getting close to the performance prior to the problems.
> 
> From b4405457f4ba07cff7b7e4f48c47668bee176a25 Mon Sep 17 00:00:00 2001
> From: Brad Campbell <brad@...rfbargle.com>
> Date: Sun, 8 Nov 2020 12:00:03 +1100
> Subject: [PATCH] hwmon: (applesmc) Re-work SMC comms
> 
> 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.
> 
> Tested on : MacbookAir6,2 MacBookPro11,1 iMac12,2, MacBookAir1,1,
> MacBookAir3,1
> 
> Fixes: fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
> Reported-by: Andreas Kemnade <andreas@...nade.info>
> Tested-by: Andreas Kemnade <andreas@...nade.info> # MacBookAir6,2
> Acked-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Brad Campbell <brad@...rfbargle.com>
> Signed-off-by: Henrik Rydberg <rydberg@...math.org>
> 
> ---
> Changelog : 
> v1 : Inital attempt
> v2 : Address logic and coding style
> v3 : Removed some debug hangover. Added tested-by. Modifications for MacBookAir1,1
> v4 : Do not expect busy state to appear without other state changes
> 

still works here (MacBookAir6,2)

Regards,
Andreas