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Date: Tue, 10 Jan 2017 13:28:36 +0200 From: Ville Syrjälä <ville.syrjala@...ux.intel.com> To: Takashi Iwai <tiwai@...e.de> Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] drm: Fix broken VT switch with video=1366x768 option 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@...r.kernel.org> > Signed-off-by: Takashi Iwai <tiwai@...e.de> > --- > 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@...ux.intel.com> > drm_mode_set_crtcinfo(mode, CRTC_INTERLACE_HALVE_V); > return mode; > } > -- > 2.11.0 -- Ville Syrjälä Intel OTC
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