Hello, I am using a Dell WD19TB dock with a 3440x1440 monitor. Using it at 100Hz used to work but recently I tried it again and discovered it no longer did, specifically the modeset seems to silently fail with no error message in userspace utilities like kscreen-doctor and xrandr and no output in dmesg. I found the problematic commit using git bisect to be 55eaef164174480df6827edeac15620f3cbcd52b "Handle the Synaptics HBlank expansion quirk". I found the issue to be the hblank_expasion_quirk_needs_dsc function which uses the following comparison in the current kernel tree: if (mode_hblank_period_ns(adjusted_mode) > hblank_limit) return false; with hblank_limit being earlier set as int hblank_limit = is_uhbr_sink ? 500 : 300; However, my monitor's HBLANK period in the 3440x1440@100Hz mode is exactly 300 ns as verified by this printk immediately before the problematic comparison. printk(KERN_INFO "Hello, kernel world! %i\n", mode_hblank_period_ns(adjusted_mode)); [ 38.429839] Hello, kernel world! 300 With the attached change the modeset works as expected at 100Hz. Would it be acceptable to modify the comparison from > to >= here? I'll do my best to provide any additional details you may need although that printk and '=' sign is the only kernel code I've written, so my best may not be great :). Signed-off-by: Benjamin D. Hoefs <bendhoefs@xxxxxxxxx> --- drivers/gpu/drm/i915/display/intel_dp_mst.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c index 15541932b809..052c5a67df93 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c @@ -446,7 +446,7 @@ hblank_expansion_quirk_needs_dsc(const struct intel_connector *connector, if (is_uhbr_sink && !drm_dp_is_uhbr_rate(limits->max_rate)) return false; - if (mode_hblank_period_ns(adjusted_mode) > hblank_limit) + if (mode_hblank_period_ns(adjusted_mode) >= hblank_limit) return false; return true; -- 2.46.2
