[Intel-gfx] [PATCH] drm/fbdev: Fallback to non tiled mode if all tiles not present

[Manasi Navare]

On Mon, Nov 04, 2019 at 07:48:26PM +1000, David Airlie wrote:
> On Mon, Nov 4, 2019 at 7:18 PM Daniel Vetter <daniel at ffwll.ch> wrote:
> >
> > On Thu, Oct 31, 2019 at 02:48:39PM -0700, Manasi Navare wrote:
> > > In case of tiled displays, if we hotplug just one connector,
> > > fbcon currently just selects the preferred mode and if it is
> > > tiled mode then that becomes a problem if rest of the tiles are
> > > not present.
> > > So in the fbdev driver on hotplug when we probe the client modeset,
> > > we we dont find all the connectors for all tiles, then on a connector
> > > with one tile, just fallback to the first available non tiled mode
> > > to display over a single connector.
> > >
> > > Suggested-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > Suggested-by: Dave Airlie <airlied at redhat.com>
> > > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > Cc: Dave Airlie <airlied at redhat.com>
> > > Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> >
> > Hm, should we mayb have a slight timeout first to wait for the 2nd
> > connector? Otherwise lots of flickering going on when plugging in one of
> > these screens ...
> 
> Not really,
> 
> There are 3 scenarios with the multi-cable tiled monitors. and
> non-resizeable fbdev.
> 
> a) it's plugged in at boot. both cables are detected, fbdev gets a
> full tiled mode.

Yes this works as expected

> b) it's not plugged in at boot, the user starts plugging it in, fbdev
> was inited via the panel or another monitor. fbdev won't resize.
> c) it's half plugged in at boot, then you get a non-tiled mode, and
> fbdev can't resize to tiled anyways.

In b and c, when its booted with only 1 cable connected and/or hotplugged only
one cable after boot, I fallback to fisrt available non tiled mode, does that sound good?

> 
> Also plugging in one of these multi-cable monitors piecemeal is going
> to take multiple seconds for the user to do physical cable plugging.

So still good with ignoring the second hotplug completely?
However i donno where in the fb helper to stop passing the modeset down
after the drm_fb_helper_hotplug_event()

Any suggestions?

Regards
Manasi

> 
> Dave.
>