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? 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
