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

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Date:   Wed, 4 Nov 2020 20:43:42 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Brad Campbell <brad@...rfbargle.com>,
        Andreas Kemnade <andreas@...nade.info>,
        Jean Delvare <jdelvare@...e.com>
Cc:     Arnd Bergmann <arnd@...db.de>, rydberg@...math.org,
        linux-hwmon@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        hns@...delico.com
Subject: Re: [REGRESSION] hwmon: (applesmc) avoid overlong udelay()

On 11/4/20 6:18 PM, Brad Campbell wrote:
> On 5/11/20 12:20 am, Andreas Kemnade wrote:
>> On Tue, 3 Nov 2020 16:56:32 +1100
>> Brad Campbell <brad@...rfbargle.com> wrote:
> 
>>> If anyone with a Mac having a conventional SMC and seeing issues on 5.9 could test this it'd be appreciated. I'm not saying this code is "correct", but it "works for me".
>>>
>> Seems to work here.
>>   dmesg  | grep applesmc
>>
>> [    1.350782] applesmc: key=561 fan=1 temp=33 index=33 acc=0 lux=2 kbd=1
>> [    1.350922] applesmc applesmc.768: hwmon_device_register() is deprecated. Please convert the driver to use hwmon_device_register_with_info().
>> [   17.748504] applesmc: wait_status looping 2: 0x4a, 0x4c, 0x4f
>> [  212.008952] applesmc: wait_status looping 2: 0x44, 0x40, 0x4e
>> [  213.033930] applesmc: wait_status looping 2: 0x44, 0x40, 0x4e
>> [  213.167908] applesmc: wait_status looping 2: 0x44, 0x40, 0x4e
>> [  219.087854] applesmc: wait_status looping 2: 0x44, 0x40, 0x4e
>>
>> Tested it on top of 5.9
> 
> Much appreciated Andreas.
> 
> I'm not entirely sure where to go from here. I'd really like some wider testing before cleaning this up and submitting it. It puts extra checks & constraints on the comms with the SMC that weren't there previously.
> 
> I guess given there doesn't appear to have been a major outcry that the driver broke in 5.9 might indicate that nobody is using it, or that it only broke on certain machines?
> 
> Can we get some guidance from the hwmon maintainers on what direction they'd like to take? I don't really want to push this forward without broader testing only to find it breaks a whole heap of machines on the basis that it fixes mine.
> 

Trick question ;-).

I'd suggest to keep it simple. Your patch seems to be quite complicated
and checks a lot of bits. Reducing that to a minimum would help limiting
the risk that some of those bits are interpreted differently on other
systems.

Guenter