On Tue, Jan 31, 2023 at 05:00:30PM +0200, Ville Syrjälä wrote:
> On Mon, Jan 16, 2023 at 01:19:37PM +0200, Stanislav Lisovskiy wrote:
> > According to spec, we should check if output_bpp * pixel_rate is less
> > than DDI clock * 72, if UHBR is used.
> >
> > HSDES: 1406899791
> > BSPEC: 49259
> >
> > v2: - Removed wrong comment(Rodrigo Vivi)
> > - Added HSDES to the commit msg(Rodrigo Vivi)
> > - Moved UHBR check to the MST specific code
> >
> > v3: - Changed commit subject(Rodrigo Vivi)
> > - Fixed the error message if check fails(Rodrigo Vivi)
> >
> > v4: - Move UHBR check to new helper function
> > - Now both for non-DSC/DSC we use that new check as
> > one of the constraints, when figuring out output bpp
> > to be used(Ville Syrjälä)
> >
> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/display/intel_dp_mst.c | 13 ++++++++++++-
> > 1 file changed, 12 insertions(+), 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 e3e7c305fece..b95051fed23d 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > @@ -47,8 +47,19 @@
> >
> > static int intel_dp_mst_check_constraints(struct drm_i915_private *i915, int bpp,
> > const struct drm_display_mode *adjusted_mode,
> > - struct intel_crtc_state *crtc_state)
> > + struct intel_crtc_state *pipe_config)
> > {
> > + if (intel_dp_is_uhbr(pipe_config)) {
> > + int output_bpp = bpp;
> > +
> > + if (output_bpp * adjusted_mode->crtc_clock >=
> > + pipe_config->port_clock * 72) {
>
> This seems to be some DSC specific constraint, but this code appears to
> apply it also to uncompresed output.
Was thinking about that. Looking at the initial HSD, also to the DSC page
in the BSpec, I have a strong feeling that this applies to any output bpp,
regardless if its compressed or not.
So decided to make this check more generic. I think this is a just general
Link BW limitation which just happened to be mentioned on DSC page.
I will clarify that.
>
> Also DDICLK != port_clock, so this looks to be off by quite a lot.
Any hints, what should I use instead?..
Stan
>
>
> > + drm_dbg_kms(&i915->drm, "UHBR check failed(required bw %d available %d)\n",
> > + output_bpp * adjusted_mode->crtc_clock, pipe_config->port_clock * 72);
> > + return -EINVAL;
> > + }
> > + }
> > +
> > return 0;
> > }
> >
> > --
> > 2.37.3
>
> --
> Ville Syrjälä
> Intel
