Re: [PATCH 2/2] drm/i915/dp: Clamp the connector max_bpc request to the valid pipe bpp range

[Imre Deak <imre.deak@intel.com>]

On Wed, Feb 11, 2026 at 09:36:55PM +0530, Nautiyal, Ankit K wrote:
> 
> On 2/11/2026 5:28 PM, Imre Deak wrote:
> > The user's request for a maximum BPC - via the max-bpc connector
> > property - determines the pipe BPP selected by the encoder, which is in
> > turn used either as the uncompressed output BPP or as the input BPP for
> > the DSC engine. This user-requested BPC->BPP can be outside of the
> > source/sink's supported valid min/max pipe BPP range and atm such an
> > out-of-bound request will be rejected by the encoder's state
> > computation.
> > 
> > As opposed to the above, the semantic for the max-bpc connector property
> > - which the user may reasonably expect - is not to fail the modeset in
> > case of an out-of-bound max BPC request, rather to adjust the request
> > clamping it to the valid BPP range.
> > 
> > Based on the above, calculate the baseline (i.e. the non-DP specific
> > platform/EDID) _maximum_ pipe BPP, storing it in
> > intel_crtc_state::max_pipe_bpp, separately from the baseline _target_
> > pipe BPP (which is the lower BPP of the baseline maximum and requested
> > BPP, stored in intel_crtc_state::pipe_bpp). This allows the encoder
> > state computation to use the baseline maximum pipe BPP as a hard limit
> > for the selected pipe BPP, while also letting it use the baseline target
> > pipe BPP only as a preference, clamping this target BPP to the valid
> > DP pipe BPP range.
> > 
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >   drivers/gpu/drm/i915/display/intel_display.c  | 12 ++++++++++
> >   .../drm/i915/display/intel_display_types.h    |  1 +
> >   drivers/gpu/drm/i915/display/intel_dp.c       | 24 +++++++++++++++++--
> >   3 files changed, 35 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > index ab4b59916d2e7..dae7a7d11cb84 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > @@ -4374,12 +4374,24 @@ compute_sink_pipe_bpp(const struct drm_connector_state *conn_state,
> >   	struct intel_display *display = to_intel_display(crtc_state);
> >   	struct drm_connector *connector = conn_state->connector;
> >   	const struct drm_display_info *info = &connector->display_info;
> > +	int edid_bpc = info->bpc ? : 8;
> >   	int target_pipe_bpp;
> > +	int max_edid_bpp;
> > +
> > +	max_edid_bpp = bpc_to_bpp(edid_bpc);
> > +	if (max_edid_bpp < 0)
> > +		return max_edid_bpp;
> >   	target_pipe_bpp = bpc_to_bpp(conn_state->max_bpc);
> >   	if (target_pipe_bpp < 0)
> >   		return target_pipe_bpp;
> > +	/*
> > +	 * The maximum pipe BPP is the minimum of the max platform BPP and
> > +	 * the max EDID BPP.
> > +	 */
> > +	crtc_state->max_pipe_bpp = min(crtc_state->pipe_bpp, max_edid_bpp);
> 
> The function compute_sink_pipe_bpp() is actually just limiting the pipe_bpp
> to sink max limits.

It limits the platform maximum pipe BPP passed to the function via
intel_crtc_state::pipe_bpp to the maximum EDID BPP _and_ the connector's
requested max-bpc x 3.

> Instead of filling the crtc_state->max_pipe_bpp in this function itself, can
> we have a separate function only to set the crtc_state->max_pipe_bpp from
> the edid max:
> compute_max_pipe_bpp(const struct drm_connector_state *conn_state,
>                      struct intel_crtc_state *crtc_state)
> 
> This can be called separately from compute_baseline_pipe_bpp:
> 
> ret = compute_max_pipe_bpp(connector_state, crtc_state);
> if (ret)
>     return ret;
> 
> ret = compute_sink_pipe_bpp(connector_state, crtc_state);
> ...
> 
> This way the compute_sink_pipe_bpp will only do one thing(adjusting the
> pipe_bpp to sink limits).
> 
> ˚oO(Perhaps we should name it to adjust_pipe_bpp_for_sink()).

Not sure. It's also good to see in one place how the debug-printed
max/target/edid BPPs are calculated.

In any case compute_sink_pipe_bpp() did compute both the target and max
BPPs implicitly even before, combining these to
intel_crtc_state::pipe_bpp, and this patch didn't change that. If
separate functions make more sense that should be a separate follow-up
change imo.

> > +
> >   	if (target_pipe_bpp < crtc_state->pipe_bpp) {
> >   		drm_dbg_kms(display->drm,
> >   			    "[CONNECTOR:%d:%s] Limiting target display pipe bpp to %d "
> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> > index e6298279dc892..e8e4af03a6a6c 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> > @@ -1163,6 +1163,7 @@ struct intel_crtc_state {
> >   	} dsi_pll;
> >   	int max_link_bpp_x16;	/* in 1/16 bpp units */
> > +	int max_pipe_bpp;	/* in 1 bpp units */
> >   	int pipe_bpp;		/* in 1 bpp units */
> >   	int min_hblank;
> >   	struct intel_link_m_n dp_m_n;
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 48845899298e4..4018b0122e8e0 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -1769,7 +1769,7 @@ static int intel_dp_max_bpp(struct intel_dp *intel_dp,
> >   	struct intel_connector *connector = intel_dp->attached_connector;
> >   	int bpp, bpc;
> > -	bpc = crtc_state->pipe_bpp / 3;
> > +	bpc = crtc_state->max_pipe_bpp / 3;
> >   	if (intel_dp->dfp.max_bpc)
> >   		bpc = min_t(int, bpc, intel_dp->dfp.max_bpc);
> > @@ -2726,7 +2726,7 @@ intel_dp_compute_config_limits(struct intel_dp *intel_dp,
> >   		 * previously. This hack should be removed once we have the
> >   		 * proper retry logic in place.
> >   		 */
> > -		limits->pipe.max_bpp = min(crtc_state->pipe_bpp, 24);
> > +		limits->pipe.max_bpp = min(crtc_state->max_pipe_bpp, 24);
> >   	} else {
> >   		limits->pipe.max_bpp = intel_dp_max_bpp(intel_dp, crtc_state,
> >   							respect_downstream_limits);
> > @@ -2757,6 +2757,26 @@ intel_dp_compute_config_limits(struct intel_dp *intel_dp,
> >   	if (dsc && !intel_dp_dsc_compute_pipe_bpp_limits(connector, limits))
> >   		return false;
> > +	/*
> > +	 * crtc_state->pipe_bpp is the non-DP specific baseline (platform/EDID)
> > +	 * maximum pipe BPP limited by the max-BPC connector property request.
> > +	 * Since by now pipe.max_bpp is <= the above baseline BPP, the only
> 
> Hmm I think I am missing something. Till now we have set pipe.max_bpp using
> crtc_state->max_pipe_bpp.

Yes and then also reducing pipe.max_bpp further by every other source
and sink maximum BPP limits.

> This is set using min of max platform Bpp and the max edid bpp (and DP dfp
> considerations, DSC sink input bpp cap).
> 
> So the relationship between pipe.max_bpp and the crtc_state->max_pipe_bpp is
> not yet clear.

The relationship is:

crtc_state->max_pipe_bpp = min(platform_max_bpp, sink_edid_max_bpp);
limits->pipe.max_bpp = min(crtc_state->max_pipe_bpp,
			   dfp_max_bpp, vbt_edp_max_bpp,
			   sink_dsc_input_max_bpp,
			   src_dsc_input_max_bpp,
			   mst_max_24bpp);

> I do agree with the rest of the below: we need to clamp the
> limits.pipe.max_bpp between crtc_state->pipe_bpp  and limit.pipe->min_bpp.

crtc_state->pipe_bpp = min(crtc_state->max_pipe_bpp, requested_bpc * 3);

and so

limits->pipe.max_bpp should be set to crtc_state->pipe_bpp clamped
between limits->pipe.min_bpp and limits->pipe.max_bpp.

> Regards,
> 
> Ankit
> 
> > +	 * remaining reason for adjusting pipe.max_bpp is the max-BPC connector
> > +	 * property request. Adjust pipe.max_bpp to this request within the
> > +	 * current valid pipe.min_bpp .. pipe.max_bpp range.
> > +	 */
> > +	limits->pipe.max_bpp = clamp(crtc_state->pipe_bpp, limits->pipe.min_bpp,
> > +				     limits->pipe.max_bpp);
> > +	if (dsc)
> > +		limits->pipe.max_bpp = align_max_sink_dsc_input_bpp(connector,
> > +								    limits->pipe.max_bpp);
> > +
> > +	if (limits->pipe.max_bpp != crtc_state->pipe_bpp)
> > +		drm_dbg_kms(display->drm,
> > +			    "[CONNECTOR:%d:%s] Adjusting requested max pipe bpp %d -> %d\n",
> > +			    connector->base.base.id, connector->base.name,
> > +			    crtc_state->pipe_bpp, limits->pipe.max_bpp);
> > +
> >   	if (is_mst || intel_dp->use_max_params) {
> >   		/*
> >   		 * For MST we always configure max link bw - the spec doesn't