Re: [PATCHv3] w1: omap-hdq: Simplify driver with PM runtime autosuspend

H. Nikolaus Schaller
2020-04-20T21:11:36Z

Hi Tony,

> Am 20.04.2020 um 17:08 schrieb Tony Lindgren <tony@atomide.com>:
>
> * H. Nikolaus Schaller <hns@goldelico.com> [200417 21:04]:
>> To me it looks as if reading hqd too quickly after omap_hdq_runtime_resume()
>> may be part of the problem, although it is 0.4 seconds between [ 18.355163]
>> and [ 18.745269]. So I am not sure about my interpretation.
>>
>> A different attempt for interpretation may be that trying to read the
>> slave triggers omap_hdq_runtime_resume() just before doing the
>> first hdq_read_byte().
>
> Hmm so I wonder if adding msleep(100) at the end of
> omap_hdq_runtime_resume() might help?

I have tried and initially it did boot and work once.
But after the second boot/reboot the effect was back.

This is something I have observed previously, that the issue
is there in ca. 9 or 10 boot attempts. So I would assume
some race condition with udev reading the uevent file of the
bq27xxx bus client and hence through hdq.

I already had noticed some hqd_read activity right after probing
success.

I had also tried to change pm_runtime_set_autosuspend_delay(, 1000)
with no success. And I tried to call omap_hdq_runtime_resume() at the
end of probe.

The only maybe important observation was when I disabled all
kernel modules except *hdq*.ko and *bq27*.ko. Then I did only
get an emergency shell so that it is quite similar to the
scenario Andreas has tested. With this setup it did work.

I then tried to reenable other kernel modules but the result
wasn't convincing that it gives a reliable result.

So I have still no clear indication when the problem occurs and
when not.

BR and thanks,
Nikolaus