linux-kernel - Re: solo6010 modprobe lockup since e1ceb25a (v4.3 regression)

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Message-ID: <20160921134554.s3tdolyej6r2w5wh@zver>
Date:   Wed, 21 Sep 2016 16:45:54 +0300
From:   Andrey Utkin <andrey_utkin@...tmail.com>
To:     Krzysztof Hałasa <khalasa@...p.pl>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Andrey Utkin <andrey.utkin@...p.bluecherry.net>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Ismael Luceno <ismael@...ev.co.uk>,
        Bluecherry Maintainers <maintainers@...echerrydvr.com>
Subject: Re: solo6010 modprobe lockup since e1ceb25a (v4.3 regression)

On Wed, Sep 21, 2016 at 03:16:57PM +0200, Krzysztof Hałasa wrote:
> Hans Verkuil <hverkuil@...all.nl> writes:
> 
> > That was probably the reason for the pci_read_config_word in the reg_write
> > code. Try putting that back (and just that).
> 
> Yes. I guess a single pci_read_config_word() would suffice.
> 
> Though it would obviously be much better to identify the place in the
> driver which needs to have the write buffers flushed, and add a read()
> just there.
> 
> The interrupt handler maybe (e.g. just before the return IRQ_HANDLED)?
> 
> OTOH this may be some sort of timing problem, I mean the faster code may
> put too much stress on the SOLO chip.
> 
> Doesn't happen here so I can't test the cure.

It happens in solo_disp_init at uploading default motion thresholds
array.

I've got a prints trace with solo6010-fix-lockup branch
https://github.com/bluecherrydvr/linux/tree/solo6010-fix-lockup/drivers/media/pci/solo6x10
the trace itself in jpg:
https://decent.im:5281/upload/3793f393-e285-4514-83dd-bf08d1c8b4a2/e7ad898b-515b-4522-86a9-553daaeb0860.jpg

Indeed, targeted fixing would be more reasonable than making register
r/w routines follow blocking fashion. But the driver is already complete
and was known to be working, and I seems all places in code assume the
blocking fashion of reg r/w, and changing that assumption may lead to
covert bugs anywhere else, not just at probing, which may be hard to
nail down.

For now, I'll try setting pci_read_config_word() back instead of full
revert. Does it need to be just in reg_write? No need for it in
reg_read, right?