linux-kernel - Re: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy for a long time

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Message-ID: <20200427151234.GE3464906@ulmo>
Date:   Mon, 27 Apr 2020 17:12:34 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jon Hunter <jonathanh@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Manikanta Maddireddy <mmaddireddy@...dia.com>,
        Vidya Sagar <vidyas@...dia.com>, linux-i2c@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy
 for a long time

On Mon, Apr 27, 2020 at 05:21:30PM +0300, Dmitry Osipenko wrote:
> 27.04.2020 14:00, Thierry Reding пишет:
> > On Mon, Apr 27, 2020 at 12:52:10PM +0300, Dmitry Osipenko wrote:
> >> 27.04.2020 10:48, Thierry Reding пишет:
> >> ...
> >>>> Maybe but all these other problems appear to have existed for sometime
> >>>> now. We need to fix all, but for the moment we need to figure out what's
> >>>> best for v5.7.
> >>>
> >>> To me it doesn't sound like we have a good handle on what exactly is
> >>> going on here and we're mostly just poking around.
> >>>
> >>> And even if things weren't working quite properly before, it sounds to
> >>> me like this patch actually made things worse.
> >>
> >> There is a plenty of time to work on the proper fix now. To me it sounds
> >> like you're giving up on fixing the root of the problem, sorry.
> > 
> > We're at -rc3 now and I haven't seen any promising progress in the last
> > week. All the while suspend/resume is now broken on at least one board
> > and that may end up hiding any other issues that could creep in in the
> > meantime.
> > 
> > Furthermore we seem to have a preexisting issue that may very well
> > interfere with this patch, so I think the cautious thing is to revert
> > for now and then fix the original issue first. We can always come back
> > to this once everything is back to normal.
> > 
> > Also, people are now looking at backporting this to v5.6. Unless we
> > revert this from v5.7 it may get picked up for backports to other
> > kernels and then I have to notify stable kernel maintainers that they
> > shouldn't and they have to back things out again. That's going to cause
> > a lot of wasted time for a lot of people.
> > 
> > So, sorry, I disagree. I don't think we have "plenty of time".
> 
> There is about a month now before the 5.7 release. It's a bit too early
> to start the panic, IMO :)

There's no panic. A patch got merged and it broken something, so we
revert it and try again. It's very much standard procedure.

> Jon already proposed a reasonable simple solution: to keep PCIe
> regulators always-ON. In a longer run we may want to have I2C atomic
> transfers supported for a late suspend phase.

That's not really a solution, though, is it? It's just papering over
an issue that this patch introduced or uncovered. I'm much more in
favour of fixing problems at the root rather than keep papering over
until we loose track of what the actual problems are.

Thierry

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