[PATCH v2] drm: Only create a cmdline mode if no probed modes match

[Radek Dostál]

On 04/20/2015 03:28 PM, 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.
> 
> A second issue sneaked into this patch is to add the cmdline mode mode
> ahead of the absolute fallback 1024x768 mode. That is if the user has
> specified a mode that we create as a fallback, we do not need to add a
> second unused fallback mode.
> 
> 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
> 
> 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

works now :)

Tested-by: Radek Dostál <rd at radekdostal.com>

Thanks,
Radek