[PATCH v3] drm: Only create a cmdline mode if no probed modes match

[Chris Wilson]

On Wed, Jun 01, 2016 at 12:43:53PM +0300, Ville Syrjälä wrote:
> On Wed, Jun 01, 2016 at 10:34:36AM +0100, Chris Wilson wrote:
> > The intention of using video=<connector>:<mode> is primarily to select
> > the user's preferred resolution at startup. Currently we always create a
> > new mode irrespective of whether the monitor has a native mode at the
> > desired resolution. This has the issue that we may then select the fake
> > mode rather the native mode during fb_helper->inital_config() and so
> > if the fake mode is invalid we then end up with a loss of signal. Oops.
> > This invalid fake mode would also be exported to userspace, who
> > potentially may make the same mistake.
> > 
> > To avoid this issue, we filter out the added command line mode if we
> > detect the desired resolution (and clock if specified) amongst the
> > probed modes. This fixes the immediate problem of adding a duplicate
> > mode, but perhaps more generically we should avoid adding a GTF mode if
> > the monitor has an EDID that is not GTF-compatible, or similarly for
> > CVT.
> > 
> > Fixes regression from
> > 
> > commit eaf99c749d43ae74ac7ffece5512f3c73f01dfd2
> > Author: Chris Wilson <chris at chris-wilson.co.uk>
> > Date:   Wed Aug 6 10:08:32 2014 +0200
> > 
> >     drm: Perform cmdline mode parsing during connector initialisation
> > 
> > that breaks HDMI output on BeagleBone Black with LG TV (model 19LS4R-ZA).
> > 
> > v2: Explicitly delete our earlier cmdline mode
> > v3: Mode pruning should now be sufficient to delete stale cmdline modes
> > 
> > Reported-by: Radek Dostál <rd at radekdostal.com>
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Radek Dostál <rd at radekdostal.com>
> > Cc: Jesse Barnes <jbarnes at virtuousgeek.org>
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > Cc: dri-devel at lists.freedesktop.org
> > Cc: Julia Lemire <jlemire at matrox.com>
> > Cc: Dave Airlie <airlied at redhat.com>
> > Cc: stable at vger.kernel.org
> > ---
> >  drivers/gpu/drm/drm_probe_helper.c | 19 +++++++++++++++++--
> >  1 file changed, 17 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> > index 0329080d7f7c..a705ed12c062 100644
> > --- a/drivers/gpu/drm/drm_probe_helper.c
> > +++ b/drivers/gpu/drm/drm_probe_helper.c
> > @@ -82,13 +82,28 @@ drm_mode_validate_flag(const struct drm_display_mode *mode,
> >  
> >  static int drm_helper_probe_add_cmdline_mode(struct drm_connector *connector)
> >  {
> > +	struct drm_cmdline_mode *cmdline_mode;
> >  	struct drm_display_mode *mode;
> >  
> > -	if (!connector->cmdline_mode.specified)
> > +	cmdline_mode = &connector->cmdline_mode;
> > +	if (!cmdline_mode->specified)
> >  		return 0;
> >  
> > +	/* Only add a GTF mode if we find no matching probed modes */
> > +	list_for_each_entry(mode, &connector->probed_modes, head) {
> > +		if (mode->hdisplay != cmdline_mode->xres ||
> > +		    mode->vdisplay != cmdline_mode->yres)
> > +			continue;
> > +
> > +		if (cmdline_mode->refresh_specified &&
> > +		    mode->vrefresh != cmdline_mode->refresh)
> 
> I think we might not have .vrefresh populated for the probed modes.
> We update .vrefresh only for the modes left on the real mode list in the
> end.

In that case, if cmdline_mode->refresh_specified keep and leave a
comment suggesting we might be able to do better :)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre