Re: [PATCH 27/27] drm: Add default modes for connectors in unknown state

From: Pekka Paalanen <ppaalanen@gmail.com>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Alex Deucher <alexdeucher@gmail.com>,
	Simon Ser <contact@emersion.fr>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Jernej Skrabec <jernej.skrabec@siol.net>,
	Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Kieran Bingham <kieran.bingham@ideasonboard.com>,
	Maling list - DRI developers  <dri-devel@lists.freedesktop.org>,
	"open list:DRM DRIVERS FOR RENESAS" 
	<linux-renesas-soc@vger.kernel.org>,
	Andrzej Hajda <a.hajda@samsung.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Sam Ravnborg <sam@ravnborg.org>
Subject: Re: [PATCH 27/27] drm: Add default modes for connectors in unknown state
Date: Fri, 26 Jun 2020 11:59:57 +0300	[thread overview]
Message-ID: <20200626115957.566efa5b@eldfell> (raw)
In-Reply-To: <CAKMK7uGF_t+zW4tyO42HN2BbV1j6fVFfVHF8Xph10bAygdsXPQ@mail.gmail.com>

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On Thu, 25 Jun 2020 12:44:36 +0200
Daniel Vetter <daniel@ffwll.ch> wrote:

> On Thu, Jun 25, 2020 at 12:32 PM Pekka Paalanen <ppaalanen@gmail.com> wrote:
> >
> > On Thu, 25 Jun 2020 09:57:44 +0200
> > Daniel Vetter <daniel@ffwll.ch> wrote:
> >  
> > > On Thu, Jun 25, 2020 at 9:56 AM Daniel Vetter <daniel@ffwll.ch> wrote:  
> > > >
> > > > On Wed, Jun 24, 2020 at 03:40:42PM -0400, Alex Deucher wrote:  

...

> > > > > No, you are right; you will have the EDID so this shouldn't be an
> > > > > issue.  I was mis-remembering the original issue.  We originally
> > > > > always reported connected for LVDS in radeon if the panel was present,
> > > > > but then we got flack because some userspace expected unknown in
> > > > > certain cases (e.g., lid or muxed displays).  Either way the EDID info
> > > > > is still there.  
> > > >
> > > > Yeah I think i915 started that habit, but I guess people realized it's
> > > > unreliable enough that they should have their own lid handler in the
> > > > desktop enviromnent doing whatever they want to do on lid close.
> > > >
> > > > Should we perhaps document that somewhere, that panels are always marked
> > > > as connected? Not even sure where to put that in the docs ...
> > > >
> > > > Maybe adding a few of the usual suspects from the compositor side, Simon,
> > > > Pekka?  
> > >
> > > Actually adding Simon and Pekka this time around ...  
> >
> > I don't know what anyone else does, but Weston (is not a DE) does not
> > look at any lid switch, and assumes that if connector status is not
> > DRM_MODE_CONNECTED, then it is disconnected. So, if a driver switched
> > to "Unknown" status, it would be taken as disconnected.  
> 
> Maybe an aside, but the guideline is for autoconfiguration:
> - Light up everything that has connector status connected.
> - If nothing has that status, try to light up the connectors with
> status "unknown".
> 
> This is only really relevant on older platforms, mostly for VGA and
> somewhat for dvi outputs.
> 
> Maybe another thing we should put down somewhere in the uapi docs ...

As I had no idea what "unknown" means or when it can happen, I assumed
that it must mean "the hardware cannot know". If the hardware cannot
know, then I certainly will not be trying to enable that, unless
explicitly configured to do so. Having a phantom output is worse than
having a real output that does not light up, because it's not obvious at
first with phantom output that anything is wrong. You may just be
wondering where your windows disappear, or where did you mouse cursor
go, or why you see a wallpaper but no login dialog, etc.

I certainly do hope no-one uses this quirk of Weston to get their lid
do what they want... it's possible, OTOH the desktop user base of
Weston according to what I've heard is around one person. It's not me.

Thanks,
pq

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