I ran into an issue with the i915 driver not being able to drive a display with this specific modeline:
[drm]] Modeline "1920x720": 60 120980 1920 1932 1936 1948 720 723 733 1035 0x48 0x9 [drm:drm_mode_prune_invalid [drm]] Not using 1920x720 mode: H_ILLEGAL After some investigation I found that intel_mode_valid (and in newer kernels, intel_cpu_transcoder_mode_valid) returns MODE_H_ILLEGAL due to (htotal - hdisplay) being lower than 32. The modeline in question indeed does not satisfy this constraint, as HTOTAL(1948) - HDISPLAY(1920) equals 28. Changing the driver code to allow for a hblank span of 28 pixels or lower resulted in the driver successfully rendering to the display. As such I propose this patch to allow for a tighter hblank span. Nb: I am uncertain if the hblank span of 32 pixels has been chosen deliberately and what the side-effects could be of lowering this value. Any insights into this or alternative solutions would be very much appreciated! I also considered introducing a kernel module parameter to optionally loosen these mode constraints. The referenced modeline is present in a line of ultrawide signage displays and has been known to work on other graphics drivers/OSes. Signed-off-by: Sebastiaan Schalbroeck <schalbro...@gmail.com> --- drivers/gpu/drm/i915/display/intel_display.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c index b10aad1..f6aba1d 100644 --- a/drivers/gpu/drm/i915/display/intel_display.c +++ b/drivers/gpu/drm/i915/display/intel_display.c @@ -7745,13 +7745,13 @@ enum drm_mode_status intel_cpu_transcoder_mode_valid(struct drm_i915_private *de */ if (DISPLAY_VER(dev_priv) >= 5) { if (mode->hdisplay < 64 || - mode->htotal - mode->hdisplay < 32) + mode->htotal - mode->hdisplay < 28) return MODE_H_ILLEGAL; if (mode->vtotal - mode->vdisplay < 5) return MODE_V_ILLEGAL; } else { - if (mode->htotal - mode->hdisplay < 32) + if (mode->htotal - mode->hdisplay < 28) return MODE_H_ILLEGAL; if (mode->vtotal - mode->vdisplay < 3) -- 2.39.2