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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 viac09dedb7a5("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:eaf99c749d("drm: Perform cmdline mode parsing during...") Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de> Link: http://patchwork.freedesktop.org/patch/msgid/20170109145614.29454-1-tiwai@suse.de Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.