drm/i915/dp_mst: Don't require DSC hblank quirk for a non-DSC compatible mode

commit 2f54e71 upstream.

If an MST branch device doesn't support DSC for a given mode, but the
MST link has enough BW for the mode, assume that the branch device does
support the mode using an uncompressed stream.

Fixes: 55eaef1 ("drm/i915/dp_mst: Handle the Synaptics HBlank expansion quirk")
Cc: stable@vger.kernel.org # v6.8+
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241009110135.1216498-2-imre.deak@intel.com
(cherry picked from commit 4e75c3e)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ideak

drivers/gpu/drm/i915/display/intel_dp_mst.c

@@ -465,6 +465,9 @@ hblank_expansion_quirk_needs_dsc(const struct intel_connector *connector,
 	if (mode_hblank_period_ns(adjusted_mode) > hblank_limit)
 		return false;
 
+	if (!intel_dp_mst_dsc_get_slice_count(connector, crtc_state))
+		return false;
+
 	return true;
 }