On Sun, Feb 18, 2024 at 07:12:24PM +0100, Bas S wrote: > I ran into an issue with the i915 driver not being able to drive a display > > with this specific modeline: >
Could you please file a bug on this? https://drm.pages.freedesktop.org/intel-docs/how-to-file-i915-bugs.html The limits below are per platform/display-architecture and probably forgotten to get updates for newer platforms. But having more information about your platform would be very helpful. Thanks, Rodrigo. > > > [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 <[1]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 > > > References > > Visible links > 1. mailto:schalbro...@gmail.com
