From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8C1BDC79F8C for ; Wed, 9 Sep 2026 04:20:47 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E296010EEA3; Wed, 9 Sep 2026 04:20:46 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="FecfI6uI"; dkim-atps=neutral Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9879510EEA3 for ; Wed, 9 Sep 2026 04:20:46 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 5983D41863; Wed, 9 Sep 2026 04:20:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 118FB1F00A3A; Wed, 9 Sep 2026 04:20:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788927646; bh=4otRgk1mpJNyLXP5BEVB1xiW5vLjJTmfPXFbRXB/NZ8=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=FecfI6uIWuXxP8UTq+Vf/MlsR1z1ShzATdgBdqWi26shjzI6lNRDHe5gvKkja+/NN X/bm1BRdjjhws22Gk03Qvmcpx2MHdoFdheeuW4hoLE/G/OX1TKVb5zbWfM44ndWtOv usp6hjP3kFe50zdTa2kpuiLzK7PspENlYJ9w3ekZ6N01tDeG1AaDHLJ43JYcwNz9bp fk0YKIkxp7IePdDQcnJrM7/987NoFDLciBjSkHDBHsmBiwbQUDodLQUd10AFt0e2jq Q2BqR0ZwFEHENJkeUDKjxFEj3YzfvOcsi6xzadf0zZEa6ZSQVhB9iaYTd6LN5vwSny V5x5LhLhBOWqg== From: sashiko-bot@kernel.org Subject: Re: [PATCH v7 1/2] drm/dp/mst: recognize DP-to-HDMI PCON as virtual DPCD in DP-to-DP topology To: "Xiao Lu" Cc: intel-gfx@lists.freedesktop.org In-Reply-To: <20260909041041.244531-1-xiaolu.xie@intel.com> References: <20260909033518.158995-1-xiaolu.xie@intel.com> <20260909041041.244531-1-xiaolu.xie@intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Wed, 09 Sep 2026 04:20:45 +0000 Message-Id: <20260909042046.118FB1F00A3A@smtp.kernel.org> X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: sashiko-reviews@lists.linux.dev Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Thank you for your contribution! Sashiko AI review found 1 potential issue(= s) to consider: - [High] drm_dp_mst_is_virtual_dpcd() unconditionally accepts DP_PEER_DEVIC= E_DP_LEGACY_CONV as a virtual DPCD without checking for a non-zero DPCD rev= ision. -- commit 7fdc1d351cc143b9e4d9acdb9eabc2fbc5bb1fee Author: Xiao Lu drm/dp/mst: recognize DP-to-HDMI PCON as virtual DPCD in DP-to-DP topology This commit attempts to correctly identify DP-to-HDMI PCON devices as having a virtual DPCD within DP-to-DP topologies. It updates the peer device check to accept legacy converters as valid downstream peer types. > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/= drm/display/drm_dp_mst_topology.c > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c [ ... ] > @@ -6047,7 +6047,8 @@ static bool drm_dp_mst_is_virtual_dpcd(struct drm_d= p_mst_port *port) > port->mstb && > port->mstb->num_ports =3D=3D 2) { > list_for_each_entry(downstream_port, &port->mstb->ports, next) { > - if (downstream_port->pdt =3D=3D DP_PEER_DEVICE_SST_SINK && > + if ((downstream_port->pdt =3D=3D DP_PEER_DEVICE_SST_SINK || > + downstream_port->pdt =3D=3D DP_PEER_DEVICE_DP_LEGACY_CONV) && > !downstream_port->input) { [Severity: High] Does this code also need to check for a non-zero DPCD revision? The commit message specifies that PCON devices indicating a virtual DPCD advertise DP_PEER_DEVICE_DP_LEGACY_CONV with a non-zero DPCD_Revision (VESA SCR Option 2). However, this new condition accepts any downstream port with the legacy converter peer type without verifying that=20 downstream_port->dpcd_rev !=3D 0. Standard legacy converters (like DP-to-VGA or standard DP-to-HDMI adapters) with an internal MST branch will typically have a DPCD revision of 0. By omitting the dpcd_rev !=3D 0 check, these standard legacy converters might = be falsely identified as having a virtual DPCD.=20 If this happens, drm_dp_mst_dsc_aux_for_port() treats the adapter as having= =20 a virtual DPCD and attempts a remote DPCD read on the legacy port. Since=20 the legacy port has no virtual DPCD, the remote DPCD read receives a NAK=20 and returns -EIO, causing drm_dp_mst_dsc_aux_for_port() to return NULL and= =20 potentially disable DSC for the port entirely. > mutex_unlock(&port->mgr->lock); > return true; > } --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260909041041.2445= 31-1-xiaolu.xie@intel.com?part=3D1