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

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Date:   Sun, 8 Nov 2020 13:04:32 +0100
From:   Henrik Rydberg <rydberg@...math.org>
To:     Brad Campbell <brad@...rfbargle.com>,
        Andreas Kemnade <andreas@...nade.info>
Cc:     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 2020-11-08 12:57, Brad Campbell wrote:
> On 8/11/20 9:14 pm, Henrik Rydberg 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.
> 
> G'day Henrik,
> 
> I like this one. It's slower on my laptop (40 rps vs 50 on the MacbookPro11,1) and the same 17 rps on the iMac 12,2 but it's as reliable
> and if it works for both of yours then I think it's a winner. I can't really diagnose the iMac properly as I'm 2,800KM away and have
> nobody to reboot it if I kill it. 5.7.2 gives 20 rps, so 17 is ok for me.
> 
> Andreas, could I ask you to test this one?
> 
> Odd my original version worked on your Air3,1 and the other 3 machines without retry.
> I wonder how many commands require retries, how many retires are actually required, and what we are going wrong on the Air1,1 that requires
> one or more retries.
> 
> I just feels like a brute force approach because there's something we're missing.

I would think you are right. There should be a way to follow the status 
changes in realtime, so one can determine handshake and processing from 
that information. At least, with this change, we are making the blunt 
instrument a little smaller.

Cheers,
Henrik