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Date:   Wed, 20 Sep 2023 19:58:00 +0100
From:   "Russell King (Oracle)" <linux@armlinux.org.uk>
To:     Doug Anderson <dianders@chromium.org>
Cc:     Maxime Ripard <mripard@kernel.org>,
        dri-devel@lists.freedesktop.org, airlied@gmail.com,
        daniel@ffwll.ch, linux-kernel@vger.kernel.org
Subject: Re: [RFT PATCH 01/15] drm/armada: Call drm_atomic_helper_shutdown()
 at shutdown time
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On Wed, Sep 20, 2023 at 11:03:32AM -0700, Doug Anderson wrote:
> Maxime,
> 
> On Wed, Sep 13, 2023 at 8:34 AM Doug Anderson <dianders@chromium.org> wrote:
> >
> > Hi,
> >
> > On Tue, Sep 5, 2023 at 7:23 AM Doug Anderson <dianders@chromium.org> wrote:
> > >
> > > Hi,
> > >
> > > On Sun, Sep 3, 2023 at 8:53 AM Russell King (Oracle)
> > > <linux@armlinux.org.uk> wrote:
> > > >
> > > > On Fri, Sep 01, 2023 at 04:41:12PM -0700, Douglas Anderson wrote:
> > > > > Based on grepping through the source code this driver appears to be
> > > > > missing a call to drm_atomic_helper_shutdown() at system shutdown
> > > > > time. Among other things, this means that if a panel is in use that it
> > > > > won't be cleanly powered off at system shutdown time.
> > > > >
> > > > > The fact that we should call drm_atomic_helper_shutdown() in the case
> > > > > of OS shutdown/restart comes straight out of the kernel doc "driver
> > > > > instance overview" in drm_drv.c.
> > > > >
> > > > > This driver was fairly easy to update. The drm_device is stored in the
> > > > > drvdata so we just have to make sure the drvdata is NULL whenever the
> > > > > device is not bound.
> > > >
> > > > ... and there I think you have a misunderstanding of the driver model.
> > > > Please have a look at device_unbind_cleanup() which will be called if
> > > > probe fails, or when the device is removed (in other words, when it is
> > > > not bound to a driver.)
> > >
> > > ...and there I think you didn't read this patch closely enough and
> > > perhaps that you have a misunderstanding of the component model.
> > > Please have a look at the difference between armada_drm_unbind() and
> > > armada_drm_remove() and also check which of those two functions is
> > > being modified by my patch. Were this patch adding a call to
> > > "dev_set_drvdata(dev, NULL)" in armada_drm_remove() then your NAK
> > > would be justified. However, I am not aware of anything in the
> > > component unbind path nor in the failure case of component bind that
> > > would NULL the drvdata.
> > >
> > > Kindly look at the patch a second time with this in mind.
> >
> > Since I didn't see any further response, I'll assume that my
> > explanation here has addressed your concerns. If not, I can re-post it
> > without NULLing the "drvdata". While I still believe this is unsafe in
> > some corner cases because of the component model used by this driver,
> > at least it would get the shutdown call in.
> >
> > In any case, what's the process for landing patches to this driver?
> > Running `./scripts/get_maintainer.pl --scm -f
> > drivers/gpu/drm/armada/armada_drv.c` seems to indicate that this
> > should go through the git tree:
> >
> > git git://git.armlinux.org.uk/~rmk/linux-arm.git drm-armada-devel
> >
> > ...but it doesn't appear that recent changes to this driver have gone
> > that way. Should this land through drm-misc?
> 
> Do you have any advice here? Should I land this through drm-misc-next,
> put it on ice for a while, or resend without the calls to NULL our the
> drvdata?

Sorry, I haven't had a chance to look at it, but I think you're probably
right, so I withdraw my objection. Please take it through drm-misc for
the time being. Thanks.

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