On Mon, Feb 09, 2026 at 05:00:13PM +0530, Nautiyal, Ankit K wrote:
>
> On 2/9/2026 3:39 PM, Imre Deak wrote:
> > On Mon, Feb 09, 2026 at 11:34:34AM +0200, Imre Deak wrote:
> > > On Mon, Feb 09, 2026 at 02:55:21PM +0530, Borah, Chaitanya Kumar wrote:
> > > >
> > > > On 2/9/2026 2:10 PM, Imre Deak wrote:
> > > > > On Mon, Feb 09, 2026 at 12:06:20PM +0530, Borah, Chaitanya Kumar
> > > > > wrote:
> > > > > >
> > > > > > On 2/6/2026 7:20 PM, Nautiyal, Ankit K wrote:
> > > > > > > On 2/6/2026 4:12 PM, Imre Deak wrote:
> > > > > > > > The pipe BPP value shouldn't be set outside of the source's /
> > > > > > > > sink's
> > > > > > > > valid pipe BPP range, ensure this when increasing the minimum
> > > > > > > > pipe BPP
> > > > > > > > value to 30 due to HDR.
> > > > > > > >
> > > > > > > > Fixes: ba49a4643cf53 ("drm/i915/dp: Set min_bpp limit to 30 in
> > > > > > > > HDR mode")
> > > > > > > > Cc: Chaitanya Kumar Borah <[email protected]>
> > > > > > > > Cc: <[email protected]> # v6.18+
> > > > > > > > Signed-off-by: Imre Deak <[email protected]>
> > > > > > > > ---
> > > > > > > > drivers/gpu/drm/i915/display/intel_dp.c | 14 ++++++++++++--
> > > > > > > > 1 file changed, 12 insertions(+), 2 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > > > > b/drivers/gpu/
> > > > > > > > drm/i915/display/intel_dp.c
> > > > > > > > index 2b8f43e211741..4d8f480cf803f 100644
> > > > > > > > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > > > > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > > > > > > > @@ -2697,6 +2697,7 @@ intel_dp_compute_config_limits(struct
> > > > > > > > intel_dp
> > > > > > > > *intel_dp,
> > > > > > > > bool dsc,
> > > > > > > > struct link_config_limits *limits)
> > > > > > > > {
> > > > > > > > + struct intel_display *display = to_intel_display(intel_dp);
> > > > > > > > bool is_mst = intel_crtc_has_type(crtc_state,
> > > > > > > > INTEL_OUTPUT_DP_MST);
> > > > > > > > struct intel_connector *connector =
> > > > > > > > to_intel_connector(conn_state->connector);
> > > > > > > > @@ -2709,8 +2710,7 @@ intel_dp_compute_config_limits(struct
> > > > > > > > intel_dp
> > > > > > > > *intel_dp,
> > > > > > > > limits->min_lane_count =
> > > > > > > > intel_dp_min_lane_count(intel_dp);
> > > > > > > > limits->max_lane_count =
> > > > > > > > intel_dp_max_lane_count(intel_dp);
> > > > > > > > - limits->pipe.min_bpp = intel_dp_in_hdr_mode(conn_state) ?
> > > > > > > > 30 :
> > > > > > > > - intel_dp_min_bpp(crtc_state->output_format);
> > > > > > > > + limits->pipe.min_bpp =
> > > > > > > > intel_dp_min_bpp(crtc_state->output_format);
> > > > > > > > if (is_mst) {
> > > > > > > > /*
> > > > > > > > * FIXME: If all the streams can't fit into the
> > > > > > > > link with their
> > > > > > > > @@ -2726,6 +2726,16 @@ intel_dp_compute_config_limits(struct
> > > > > > > > intel_dp *intel_dp,
> > > > > > > > respect_downstream_limits);
> > > > > > > > }
> > > > > > > > + if (intel_dp_in_hdr_mode(conn_state)) {
> > > > > > > > + if (limits->pipe.min_bpp <= 30 && limits->pipe.max_bpp
> > > > > > > > >= 30)
> > > > > > > > + limits->pipe.min_bpp = 30;
> > > > > > > > + else
> > > > > > > > + drm_dbg_kms(display->drm,
> > > > > > > > + "[CONNECTOR:%d:%s] HDR min 30 bpp outside
> > > > > > > > of
> > > > > > > > valid pipe bpp range (%d-%d)\n",
> > > > > > > > + connector->base.base.id,
> > > > > > > > connector->base.name,
> > > > > > > > + limits->pipe.min_bpp,
> > > > > > > > limits->pipe.max_bpp);
> > > > > > >
> > > > > > > pipe.max_bpp < 30 will be either due to the max_bpc property set
> > > > > > > to less
> > > > > > > than 10, or perhaps when the panel itself does not support 10 bpc
> > > > > > > (limited by EDID or VBT).
> > > > > > > With these constraints doesn't make sense to enable HDR and send
> > > > > > > HDR
> > > > > > > metadata.
> > > > > > > However, as we see in some reported issues [1] [2], in practice
> > > > > > > some
> > > > > > > compositor seems to enable HDR by default and with the hard limit
> > > > > > > set,
> > > > > > > they report blankout.
> > > > > > > So it does make sense to raise the min bpp limit only if its
> > > > > > > inside the
> > > > > > > supported range.
> > > > > > >
> > > > > > > Reviewed-by: Ankit Nautiyal <[email protected]>
> > > > > > >
> > > > > > >
> > > > > > > [1] https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7052
> > > > > > > [2] https://gitlab.freedesktop.org/drm/i915/kernel/-/
> > > > > > > issues/5969#note_3248404
> > > > > > >
> > > > > > I am not sure if this patch would help with the above gitlabs. For
> > > > > > example
> > > > > > in case of #7052 pipe max bpp is 30 and the commit still fails.
> > > > > It does fix though reported cases where the sink does not support 10
> > > > > BPC
> > > > > at all. Yes the monitor in #7052 is still a problem, since it supports
> > > > > 10 BPC only with lower resolution, where the link BW would allow this
> > > > > and he monitor doesn't have DSC either.
> > > > >
> > > > > > However, I need to look deeper.
> > > > > >
> > > > > > I am thinking of relaxing this restriction all together because the
> > > > > > earlier
> > > > > > assumption that a panel advertising HDR will support atleast 10bpc
> > > > > > in all
> > > > > > it's mode turns out to be false.
> > > > > >
> > > > > > Currently, I am inclined on the following policy.
> > > > > >
> > > > > > - If DSC is not available, fall back to normal bandwidth
> > > > > > calculations and
> > > > > > select the highest bpp the link can support. (Also preferred by
> > > > > > Kwin)
> > > > > >
> > > > > > - If DSC is available, prefer falling back to DSC and attempt the
> > > > > > highest
> > > > > > bpp allowed by bandwidth constraints.
> > > > > The patch does the above, except for not handling the case where the
> > > > > monitor doesn't support DSC. The attach patch handles that too and so
> > > > > fixes #7052 as well, are you ok with it?
> > > > This should work since [1] did.
> > > I think the sink / source support for 10 BPC should be still checked as
> > > in this patch.
> > >
> > > > There is one more (theoritical) scenario that I think is still not
> > > > covered.
> > > > What happens in a case where 30bpp doesnot fit into DSC bandwidth?
> > > > As I understand, the min bpp limit of 30bpp would become a bottle-neck
> > > > even
> > > > then?
> > > No, the link BW requirement is determined by the link BPP, not the pipe
> > > BPP for which the minimum is set. The link BPP in DSC mode can be
> > > lowered below that, based on the sink's minimum compressed BPP support.
> > > So in the fallback case, where 30 BPP uncompressed mode is not
> > > supported by the sink due to a BW limit, DSC is used instead lowering
> > > the compressed link BPP as required.
> > Although, it's still possible that the sink wouldn't support the minimum
> > pipe BPP set here as a DSC input BPP. Setting a minimum (pipe/input) BPP
> > in DSC mode isn't actually needed, since the highest possible BPP will
> > be selected there anyway. So I think the actual condition for setting
> > pipe.min_bpp = 30 above should be:
> >
> > if (intel_dp_in_hdr_mode(conn_state) &&
> > intel_dp_supports_dsc(intel_dp, connector, crtc_state) &&
> > !dsc) {
> > ...
>
> Hmm makes sense.
>
> Perhaps we should also add a debug message right after pipe_bpp is finalized
> (and before the full link config dump) to make it clear when HDR is selected
> but the chosen input/pipe bpp ends up below 30 bpp.
>
> Something like below, in intel_dp_compute_link_for_joined_pipes() before the
> link config dump:
>
> if (intel_dp_in_hdr_mode(conn_state) && pipe_config->pipe_bpp < 30)
> drm_dbg_kms(display->drm,
> "HDR mode selected but pipe bpp is limited to %d\n",
> pipe_config->pipe_bpp);
>
> This will help flag out the cases where HDR is enabled but the pipe can’t
> reach 10bpc due to sink or bandwidth limits.
Ok, can also debug print the connector's HDR mode, like
DP lane count ... bpp input x compressed y HDR-sink yes/no ...
at the end of intel_dp_compute_link_for_joined_pipes().
>
>
> Regards,
>
> Ankit
>
> > > > [1]
> > > > https://github.com/ckborah/drm-tip-sandbox/commit/5dd10a763ae6e651a0ab494ab1ad0c9d81c2de47
> > > >
> > > > > > I am working on a patch for this and should be able to float
> > > > > > something soon.
> > > > > > Imre, if you agree with this policy, would you please wait for the
> > > > > > patch.
> > > > > > That should make it easier to send out fix for stable kernels.
> > > > > >
> > > > > > ==
> > > > > > Chaitanya
> > > > > >
> > > > > > > > + }
> > > > > > > > +
> > > > > > > > if (dsc &&
> > > > > > > > !intel_dp_dsc_compute_pipe_bpp_limits(connector,
> > > > > > > > limits))
> > > > > > > > return false;
