[Bug 104934] Sometimes does not detect 60Hz Full HD mode for external display, switching to 60 Hz with interlace

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104934

--- Comment #5 from Martin Steigerwald <Martin at Lichtvoll.de> ---
(In reply to Jani Nikula from comment #4)
> Please add drm.debug=14 module parameter, and attach dmesg from boot to
> reproducing the problem. Thanks.

I booted with that module parameter and it appears that the driver detects the
mode but thinks its clock would be too high:

Apr  7 12:38:52 merkaba kernel: [    6.825185]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 74:"1920x1080" 60 148500 1920
2008 2052 2200 1080 1084 1089 1125 0x48 0x5
Apr  7 12:38:52 merkaba kernel: [    6.825189] [drm:drm_mode_prune_invalid
[drm]] Not using 1920x1080 mode: CLOCK_HIGH
Apr  7 12:38:52 merkaba kernel: [    6.825194]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 107:"1920x1080" 60 148352
1920 2008 2052 2200 1080 1084 1089 1125 0x40 0x5
Apr  7 12:38:52 merkaba kernel: [    6.825198] [drm:drm_mode_prune_invalid
[drm]] Not using 1920x1080 mode: CLOCK_HIGH
Apr  7 12:38:52 merkaba kernel: [    6.825203]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 76:"1920x1080" 50 148500 1920
2448 2492 2640 1080 1089 1095 1125 0x40 0xa
Apr  7 12:38:52 merkaba kernel: [    6.825207] [drm:drm_mode_prune_invalid
[drm]] Not using 1920x1080 mode: CLOCK_HIGH
Apr  7 12:38:52 merkaba kernel: [    6.825211]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 93:"1920x1080" 0 148500 1920
2448 2492 2640 1080 1084 1089 1125 0x40 0x5
Apr  7 12:38:52 merkaba kernel: [    6.825215] [drm:drm_mode_prune_invalid
[drm]] Not using 1920x1080 mode: CLOCK_HIGH
Apr  7 12:38:52 merkaba kernel: [    6.825219]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 80:"1680x1050" 0 146250 1680
1784 1960 2240 1050 1053 1059 1089 0x40 0x6
Apr  7 12:38:52 merkaba kernel: [    6.825223] [drm:drm_mode_prune_invalid
[drm]] Not using 1680x1050 mode: CLOCK_HIGH

However when I do the plug the displayport cable to the other port trick it
again accepted the 70 Hz mode:

Apr  7 12:42:15 merkaba kernel: [  210.505175]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 79:"1920x1080" 60 148500 1920
2008 2052 2200 1080 1084 1089 1125 0x48 0x5
Apr  7 12:42:15 merkaba kernel: [  210.505183]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 115:"1920x1080" 60 148352
1920 2008 2052 2200 1080 1084 1089 1125 0x40 0x5
Apr  7 12:42:15 merkaba kernel: [  210.505190]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 102:"1920x1080i" 60 74250
1920 2008 2052 2200 1080 1084 1094 1125 0x40 0x15
Apr  7 12:42:15 merkaba kernel: [  210.505197]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 120:"1920x1080i" 60 74176
1920 2008 2052 2200 1080 1084 1094 1125 0x40 0x15
Apr  7 12:42:15 merkaba kernel: [  210.505204]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 82:"1920x1080" 50 148500 1920
2448 2492 2640 1080 1089 1095 1125 0x40 0xa
Apr  7 12:42:15 merkaba kernel: [  210.505212]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 101:"1920x1080" 50 148500
1920 2448 2492 2640 1080 1084 1089 1125 0x40 0x5
Apr  7 12:42:15 merkaba kernel: [  210.505219]
[drm:drm_mode_debug_printmodeline [drm]] Modeline 103:"1920x1080i" 50 74250
1920 2448 2492 2640 1080 1084 1094 1125 0x40 0x15

I will attach two kern.log files, one with a boot into the broken state,
another one which in addition has the log messages for replugging the
displayport cable to the other port.

Please note that it does not matter whether the system boots with display
connected DP-2 or DP-3. It shows the issue with both ports. But when I replug
the cable from DP-2 to DP-3 or DP-3 to DP-2 depending on where it was connected
during boot it always accepts the Full HD 60 Hz modes. And these work very
stable.

Also note: After a suspend to ram or a hibernation cycle the 60 Hz mode still
works. It appears to me that the directly after boot mode detection is broken.

Is there a way to override the maximum usable CLOCK as a work-around? I know it
works. :)

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