On Wed, Jun 1, 2016 at 5:50 AM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> 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
> v4: Compute the vrefresh for the probed mode
Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx>
>
> Reported-by: Radek Dostál <rd@xxxxxxxxxxxxxxx>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Radek Dostál <rd@xxxxxxxxxxxxxxx>
> Cc: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: Julia Lemire <jlemire@xxxxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> drivers/gpu/drm/drm_probe_helper.c | 21 +++++++++++++++++++--
> 1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 0329080d7f7c..a0df377d7d1c 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -82,13 +82,30 @@ 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) {
> + /* The probed mode's vrefresh is set until later */
> + if (drm_mode_vrefresh(mode) != cmdline_mode->refresh)
> + continue;
> + }
> +
> + return 0;
> + }
> +
> mode = drm_mode_create_from_cmdline_mode(connector->dev,
> - &connector->cmdline_mode);
> + cmdline_mode);
> if (mode == NULL)
> return 0;
>
> --
> 2.8.1
>
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