linux-kernel - Re: [PATCH 3/3 v3] drm: bridge/dw-hdmi: Move edid reading to .detect() callback

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Message-ID: <20160805081349.GI12034@nuc-i3427.alporthouse.com>
Date:	Fri, 5 Aug 2016 09:13:49 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Russell King - ARM Linux <linux@...linux.org.uk>,
	Jose Abreu <Jose.Abreu@...opsys.com>,
	dri-devel@...ts.freedesktop.org,
	Carlos Palminha <CARLOS.PALMINHA@...opsys.com>,
	Archit Taneja <architt@...eaurora.org>,
	David Airlie <airlied@...ux.ie>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Takashi Iwai <tiwai@...e.de>,
	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>,
	Thierry Reding <treding@...dia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3 v3] drm: bridge/dw-hdmi: Move edid reading to
 .detect() callback

On Fri, Aug 05, 2016 at 10:06:08AM +0200, Daniel Vetter wrote:
> On Fri, Aug 05, 2016 at 12:01:25AM +0100, Russell King - ARM Linux wrote:
> > On Thu, Aug 04, 2016 at 06:13:18PM +0100, Jose Abreu wrote:
> > > Hi Russell,
> > > 
> > > So, I didn't use framebuffer console but used X instead and it is
> > > working as it should. I think we can drop this patch. I am now
> > > making interoperability with DVI and I am facing the following
> > > scenario:
> > >     - I start the driver
> > >     - An EDID is sent which tells the driver that HDMI is NOT
> > > supported;
> > >     - The driver configures itself to a DVI mode;
> > > 
> > > Until this point everything is working as it should. But:
> > > 
> > >     - Now I send an EDID which tells the driver that HDMI is
> > > supported;
> > >     - As the EDID has the same preferred mode the user will not
> > > reconfigure the mode and there will be no change to HDMI mode.
> > 
> > The EDID should still be read, but as you say, userspace doesn't take
> > any action because it sees that the mode parameters are still the same,
> > as you have identified.
> > 
> > > The missing change to HDMI mode will cause the test to fail. The
> > > workaround that I am using is to reconfigure to another video
> > > mode and then configure to the preferred one but I think this
> > > could be fixed in the driver, right?
> > 
> > This one is extremely awkward - to fix it, we would need to check to
> > see whether we reconfigure the hardware each time we read the EDID,
> > and I don't think that's a particularly nice thing to do.
> > 
> > I'd like to hear what other DRM developers think about this issue.
> 
> I pondored whether we should have a counter on each connector for probe
> state, which helpers would increment whenever something changes, like:
> - connector_status (as tracked by probe helpers)
> - anything in the edid changes (when setting it
>   drm_mode_connector_update_edid_property)
> - other changes (like sink state changes in dpcd or whatever)
> 
> That way userspace would be able to reliably spot such changes and do a
> new modeset.

Yes, please. I have had similar wishes for state changes and overall
modeset counters.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre