| Message ID | 20191115210728.3467-4-lyude@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | MST BPC fixes for nouveau | expand |
On Fri, Nov 15, 2019 at 04:07:20PM -0500, Lyude Paul wrote: > Noticed this while working on some unrelated CRC stuff. Currently, > userspace has very little support for BPCs higher than 8. While this > doesn't matter for most things, on MST topologies we need to be careful > about ensuring that we do our best to make any given display > configuration fit within the bandwidth restraints of the topology, since > otherwise less people's monitor configurations will work. > > Allowing for BPC settings higher than 8 dramatically increases the > required bandwidth for displays in most configurations, and consequently > makes it a lot less likely that said display configurations will pass > the atomic check. > > In the future we want to fix this correctly by making it so that we > adjust the bpp for each display in a topology to be as high as possible, > while making sure to lower the bpp of each display in the event that we > run out of bandwidth and need to rerun our atomic check. But for now, > follow the behavior that both i915 and amdgpu are sticking to. > > Signed-off-by: Lyude Paul <lyude@redhat.com> > Fixes: 232c9eec417a ("drm/nouveau: Use atomic VCPI helpers for MST") > Cc: Ben Skeggs <bskeggs@redhat.com> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > Cc: David Airlie <airlied@redhat.com> > Cc: Jerry Zuo <Jerry.Zuo@amd.com> > Cc: Harry Wentland <harry.wentland@amd.com> > Cc: Juston Li <juston.li@intel.com> > Cc: Sam Ravnborg <sam@ravnborg.org> > Cc: Sean Paul <seanpaul@chromium.org> > Cc: <stable@vger.kernel.org> # v5.1+ > --- > drivers/gpu/drm/nouveau/dispnv50/disp.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) Reviewed-by: Thierry Reding <treding@nvidia.com>
diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c index 93665aecce57..9ac47fe519f8 100644 --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c @@ -798,7 +798,14 @@ nv50_msto_atomic_check(struct drm_encoder *encoder, if (!state->duplicated) { const int clock = crtc_state->adjusted_mode.clock; - asyh->or.bpc = connector->display_info.bpc; + /* + * XXX: Since we don't use HDR in userspace quite yet, limit + * the bpc to 8 to save bandwidth on the topology. In the + * future, we'll want to properly fix this by dynamically + * selecting the highest possible bpc that would fit in the + * topology + */ + asyh->or.bpc = min(connector->display_info.bpc, 8U); asyh->dp.pbn = drm_dp_calc_pbn_mode(clock, asyh->or.bpc * 3); }
Noticed this while working on some unrelated CRC stuff. Currently, userspace has very little support for BPCs higher than 8. While this doesn't matter for most things, on MST topologies we need to be careful about ensuring that we do our best to make any given display configuration fit within the bandwidth restraints of the topology, since otherwise less people's monitor configurations will work. Allowing for BPC settings higher than 8 dramatically increases the required bandwidth for displays in most configurations, and consequently makes it a lot less likely that said display configurations will pass the atomic check. In the future we want to fix this correctly by making it so that we adjust the bpp for each display in a topology to be as high as possible, while making sure to lower the bpp of each display in the event that we run out of bandwidth and need to rerun our atomic check. But for now, follow the behavior that both i915 and amdgpu are sticking to. Signed-off-by: Lyude Paul <lyude@redhat.com> Fixes: 232c9eec417a ("drm/nouveau: Use atomic VCPI helpers for MST") Cc: Ben Skeggs <bskeggs@redhat.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: David Airlie <airlied@redhat.com> Cc: Jerry Zuo <Jerry.Zuo@amd.com> Cc: Harry Wentland <harry.wentland@amd.com> Cc: Juston Li <juston.li@intel.com> Cc: Sam Ravnborg <sam@ravnborg.org> Cc: Sean Paul <seanpaul@chromium.org> Cc: <stable@vger.kernel.org> # v5.1+ --- drivers/gpu/drm/nouveau/dispnv50/disp.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)