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Subject: Re: [PATCHv3] w1: omap-hdq: Simplify driver with PM runtime autosuspend
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From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <20200420150802.GR37466@atomide.com>
Date:   Mon, 20 Apr 2020 23:11:18 +0200
Cc:     Andreas Kemnade <andreas@kemnade.info>,
        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>
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References: <20191217004048.46298-1-tony@atomide.com> <7B8C7DD9-095B-48FC-9642-695D07B79E97@goldelico.com> <20200416184638.GI37466@atomide.com> <3197C3F0-DEB9-4221-AFBD-4F2A08C84C4C@goldelico.com> <20200417164340.3d9043d1@aktux> <6430AF54-849E-456B-8DB0-B4478BBDB78D@goldelico.com> <20200417150721.GL37466@atomide.com> <8E062482-5D5D-4837-9980-D6C708DD24D4@goldelico.com> <20200420150802.GR37466@atomide.com>
To:     Tony Lindgren <tony@atomide.com>
Sender: linux-kernel-owner@vger.kernel.org
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Hi Tony,

> Am 20.04.2020 um 17:08 schrieb Tony Lindgren <tony@atomide.com>:
>=20
> * 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.
>>=20
>> 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().
>=20
> 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