On Thu, 29 Oct 2026, Dmytro Malovanyi <[email protected]> wrote: > DP 1.2 section 2.2.1.1 says "An upstream device interoperating with a > downstream device with DPCD Revision of 1.2 or higher must enable > Enhanced Framing Mode". So for r1.2+ the DPCD revision is enough, the > DP_ENHANCED_FRAME_CAP bit does not need to be checked. > > Some sinks get this bit wrong. The Xiaomi Monitor A24i (P24FBA-RAGL) > sets it in the base receiver caps, but clears it in the extended > receiver caps at 0x2200, which are the ones we use: > > base: 12 0a c4 01 01 00 01 80 02 00 06 00 00 00 81 > extended: 14 0a 44 00 01 00 01 80 02 02 06 00 00 00 81 > > Through a USB4 dock (CalDigit Element 5) the link trains without > enhanced framing (0x202-0x204: 77 77 81), but the sink never syncs to > the stream (SINK_STATUS 0x205: 00) and shows "No signal". Forcing RBR > does not change it. Connected directly to the laptop the same sink > syncs without enhanced framing, at RBR, HBR and HBR2. > > Make drm_dp_enhanced_frame_cap() return true for DPCD r1.2+. This > changes behaviour for every driver using the helper, but only for sinks > which already violate the spec by not setting the bit. > > Tested on i915 (Arrow Lake-U), with the dock the link now uses enhanced > framing (0x101: 84) and the sink syncs (0x205: 03). > > Fixes: a1d926527b79 ("drm/i915: implement > EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT") > Cc: [email protected] > Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/17719 > Suggested-by: Jani Nikula <[email protected]> > Signed-off-by: Dmytro Malovanyi <[email protected]>
Reviewed-by: Jani Nikula <[email protected]> I've bounced the series to intel-gfx and intel-xe to get CI results, though I don't really expect any regressions. I'd appreciate acks from other driver vendors too. > --- > include/drm/display/drm_dp_helper.h | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/include/drm/display/drm_dp_helper.h > b/include/drm/display/drm_dp_helper.h > index 5b05a7fbe..4f20f60db 100644 > --- a/include/drm/display/drm_dp_helper.h > +++ b/include/drm/display/drm_dp_helper.h > @@ -160,6 +160,10 @@ drm_dp_max_lane_count(const u8 > dpcd[DP_RECEIVER_CAP_SIZE]) > static inline bool > drm_dp_enhanced_frame_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) > { > + /* DP 1.2 2.2.1.1: enhanced framing is mandatory for DPCD r1.2+ */ > + if (dpcd[DP_DPCD_REV] >= 0x12) > + return true; > + > return dpcd[DP_DPCD_REV] >= 0x11 && > (dpcd[DP_MAX_LANE_COUNT] & DP_ENHANCED_FRAME_CAP); > } -- Jani Nikula, Intel
