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Date:   Tue, 21 Apr 2020 08:53:36 +0200
From:   Andreas Kemnade <andreas@kemnade.info>
To:     "H. Nikolaus Schaller" <hns@goldelico.com>
Cc:     Tony Lindgren <tony@atomide.com>,
        Evgeniy Polyakov <zbr@ioremap.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-omap <linux-omap@vger.kernel.org>,
        Adam Ford <aford173@gmail.com>,
        "Andrew F . Davis" <afd@ti.com>, Vignesh R <vigneshr@ti.com>
Subject: Re: [PATCHv3] w1: omap-hdq: Simplify driver with PM runtime
 autosuspend
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On Mon, 20 Apr 2020 23:11:18 +0200
"H. Nikolaus Schaller" <hns@goldelico.com> wrote:

> 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.
> 
So I guess without idling uarts?

> 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.
> 
Hmm, last summer I had problems even without that patch reading
temperature while doing umts transfers. Maybe there are some
connections,
maybe not. For that scenario we might have emc issues, thermal problems
or a real kernel problem.

Regards,
Andreas