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Ville Syrjälä 2682768bde drm/edid: Fixup h/vsync_end instead of h/vtotal There are some weird EDIDs floating around that have the sync pulse extending beyond the end of the blanking period. On the currently problemtic machine (HP Omni 120) EDID reports the following mode: "1600x900": 60 108000 1600 1780 1860 1800 900 910 913 1000 0x40 0x5 which is then "corrected" to have htotal=1861 by the current drm_edid.c code. The fixup code was originally added in commit `7064fef563` ("drm: work around EDIDs with bad htotal/vtotal values"). Googling around we end up in https://bugs.launchpad.net/ubuntu/hardy/+source/xserver-xorg-video-intel/+bug/297245 where we find an EDID for a Dell Studio 15, which reports: (II) VESA(0): clock: 65.0 MHz Image Size: 331 x 207 mm (II) VESA(0): h_active: 1280 h_sync: 1328 h_sync_end 1360 h_blank_end 1337 h_border: 0 (II) VESA(0): v_active: 800 v_sync: 803 v_sync_end 809 v_blanking: 810 v_border: 0 Note that if we use the hblank size (as opposed of the hsync_end) from the DTD to determine htotal we get exactly 60Hz refresh rate in both cases, whereas using hsync_end to determine htotal we get a slightly lower refresh rates. This makes me believe the using the hblank size is what was intended even in those cases. Also note that in case of the HP Onmi 120 the VBIOS boots with these: crtc timings: 108000 1600 1780 1860 1800 900 910 913 1000, type: 0x40 flags: 0x5 ie. it just blindly stuffs the bogus hsync_end and htotal from the DTD into the transcoder timing registers, and the display works. I believe the (at least more modern) hardware will automagically terminate the hsync pulse when the timing generator reaches htotal, which again points that we should use the hblank size to determine htotal. Unfortunatley the old bug reports for the Dell machines are extremely lacking in useful details so we have no idea what kind of timings the VBIOS programmed into the hardware :( Let's just flip this quirk around and reduce the length of the sync pulse instead of extending the blanking period. This at least seems to be the correct thing to do on more modern hardware. And if any issues crop up on older hardware we need to debug them properly. v2: Add debug message breadcrumbs (Jani) Reviewed-by: Jani Nikula <jani.nikula@intel.com> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/8895 Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20230920211934.14920-1-ville.syrjala@linux.intel.com		History 2023-09-21 22:06:17 +03:00
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README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
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There are various text files in the Documentation/ subdirectory,
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Please read the Documentation/process/changes.rst file, as it contains the
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the problems which may result by upgrading your kernel.