On Fri, Oct 30, 2026 at 01:36:31PM +0200, Jani Nikula wrote: > On Fri, 30 Oct 2026, Ville Syrjälä <[email protected]> wrote: > > On Thu, Oct 29, 2026 at 11:18:22AM +0100, Dmytro Malovanyi 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]> > >> --- > >> 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+ */ > > > > DP_ENHANCED_FRAME_CAP is also mandatory so I think this needs > > a bit more detailed explanation. > > Commit message not enough?
On its face the check looks completely redundant, so without further justification someone is likely to just remove it. > > I think the wording in the specs suggest that with DPCD r1.2+ you should > just enable enhanced framing regardless of the cap. > > BR, > Jani. > > > > >> + if (dpcd[DP_DPCD_REV] >= 0x12) > >> + return true; > >> + > >> return dpcd[DP_DPCD_REV] >= 0x11 && > >> (dpcd[DP_MAX_LANE_COUNT] & DP_ENHANCED_FRAME_CAP); > >> } > >> -- > >> 2.50.1 (Apple Git-155) > > -- > Jani Nikula, Intel -- Ville Syrjälä Intel
