>> I can't guarantee it won't break older machines which is why I've 
>> asked for help testing it. I only have a MacbookPro 11,1 and an iMac 
>> 12,2. It fixes both of those.
>>
>> Help testing would be much appreciated.
> 
> I see, this makes much more sense. I may be able to run some tests 
> tonight. Meanwhile, looking at the patch, the status variable in 
> send_command looks superfluous now that there is a wait_status() before it.

Ok, it took some time to get the machines up to speed, but so far I have 
managed to run some tests on an MacBookAir1,1. I only managed to upgrade 
up to 4.15, so I had to revert the inputdev polling patch, but the rest 
applied without problems. I recovered an old test program I used to use 
(attached), and checked for failures and reads per second

*** hwmon: (applesmc) switch to using input device polling mode

At this point in the tree, with this reverted, I see 0 failures and 55 
reads per second.

*** hwmon: (applesmc) avoid overlong udelay()

With this applied, I see 0 failures and 16 reads per second.

*** hwmon: (applesmc) check status earlier.

With this applied, I see 0 failures and 16 reads per second.

*** (HEAD -> stable) applesmc: Re-work SMC comms v2

With this applied, the kernel hangs in module probe, and the kernel log 
is flooded with read failures.

So as it stands, it does not work at all. I will continue to check 
another machine, and see if I can get something working.

Henrik