On Mon, Jan 09, 2017 at 03:56:14PM +0100, Takashi Iwai wrote:
> I noticed that the VT switch doesn't work any longer with a Dell
> laptop with 1366x768 eDP when the machine is connected with a DP
> monitor. It behaves as if VT were switched, but the graphics remain
> frozen. Actually the keyboard works, so I could switch back to VT7
> again.
>
> I tried to track down the problem, and encountered a long story until
> we reach to this error:
>
> - The machine is booted with video=1366x768 option (the distro
> installer seems to add it as default).
> - Recently, drm_helper_probe_single_connector_modes() deals with
> cmdline modes, and it tries to create a new mode when no
> matching mode is found.
> - The drm_mode_create_from_cmdline_mode() creates a mode based on
> either CVT of GFT according to the given cmdline mode; in our case,
> it's 1366x768.
> - Since both CVT and GFT can't express the width 1366 due to
> alignment, the resultant mode becomes 1368x768, slightly larger than
> the given size.
> - Later on, the atomic commit is performed, and in
> drm_atomic_check_only(), the size of each plane is checked.
> - The size check of 1366x768 fails due to the above, and eventually
> the whole VT switch fails.
>
> Back in the history, we've had a manual fix-up of 1368x768 in various
> places via c09dedb7a50e ("drm/edid: Add a workaround for 1366x768 HD
> panel"), but they have been all in drm_edid.c at probing the modes
> from EDID. For addressing the problem above, we need a similar hack
> to the mode newly created from cmdline, manually adjusting the width
> when the expected size is 1366 while we get 1368 instead.
>
> Fixes: eaf99c749d43 ("drm: Perform cmdline mode parsing during...")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> ---
> drivers/gpu/drm/drm_modes.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index ac6a35212501..e6b19bc9021a 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1460,6 +1460,13 @@ drm_mode_create_from_cmdline_mode(struct drm_device *dev,
> return NULL;
>
> mode->type |= DRM_MODE_TYPE_USERDEF;
> + /* fix up 1368x768: GFT/CVT can't express 1366 width due to alignment */
> + if (cmd->xres == 1366 && mode->hdisplay == 1368) {
> + mode->hdisplay = 1366;
> + mode->hsync_start--;
> + mode->hsync_end--;
> + drm_mode_set_name(mode);
> + }
Maybe give fixup_mode_1366x768() a drm_ prefix and make in non-static to
avoid duplicating the code? And I guess move it to drm_modes.c?
Otherwise lgtm:
Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> drm_mode_set_crtcinfo(mode, CRTC_INTERLACE_HALVE_V);
> return mode;
> }
> --
> 2.11.0
--
Ville Syrjälä
Intel OTC
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