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a="1898024" X-IronPort-AV: E=Sophos;i="6.27,184,1787036400"; d="scan'208";a="1898024" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Oct 2026 04:54:21 -0700 X-CSE-ConnectionGUID: +A58QkJcTMik+42R32X5Cw== X-CSE-MsgGUID: RDmo4aLCReW6b8SBGQAJbQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,184,1787036400"; d="scan'208";a="5218611" Received: from pgcooper-mobl3.ger.corp.intel.com (HELO localhost) ([10.245.245.145]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Oct 2026 04:54:12 -0700 From: Jani Nikula To: Dmytro Malovanyi , dri-devel@lists.freedesktop.org Cc: Ville =?utf-8?B?U3lyasOkbMOk?= , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Harry Wentland , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Luca Ceresoli , Patrik Jakobsson , Lyude Paul , Danilo Krummrich , nouveau@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, Dmytro Malovanyi , Harry Wentland , Leo Li Subject: Re: [PATCH v2 1/5] drm/dp: Always use enhanced framing for DPCD r1.2+ In-Reply-To: <20261029101826.72773-2-dmitrymalovanyy@gmail.com> Organization: Intel Finland Oy - BIC 0357606-4 - c/o Alberga Business Park, 6 krs Bertel Jungin Aukio 5, 02600 Espoo, Finland References: <20261029101826.72773-1-dmitrymalovanyy@gmail.com> <20261029101826.72773-2-dmitrymalovanyy@gmail.com> Date: Thu, 29 Oct 2026 13:54:09 +0200 Message-ID: <5c241fa804e1e4ea4518854a96097252f7a5317a@intel.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain On Thu, 29 Oct 2026, 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: stable@vger.kernel.org > Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/17719 > Suggested-by: Jani Nikula > Signed-off-by: Dmytro Malovanyi Reviewed-by: Jani Nikula 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