From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B5EB5606A327 for ; Sat, 14 Nov 2026 05:26:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=STRTzdeU Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 1E90710ECAF; Sat, 14 Nov 2026 05:26:06 +0000 (UTC) Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 1A71D10ED42 for ; Sat, 14 Nov 2026 05:25:59 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 9F0B141B45; Sat, 14 Nov 2026 05:25:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 44D6E1F000C4; Sat, 14 Nov 2026 05:25:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794633958; bh=luTjNUmmW3tuVeZr3g+JBk8K6v1ke+HbANcumBiXx00=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=STRTzdeUG2CxWVONaXrYoR7XqfYbNrHAJctjheXSHVBmPCZSQMWy0A0E8dUjtbQOi ryKJlHMnZ8ikwD8JAWw2ebgFBUJ0ASQGmApwWrEBILkvl764bll14PJg+P0fGAPegx ZZqKHgW66y1rKyXJE3aW74PZEqLTfCRzHmFaSzZsZPn60fnsn+q2Eig1nAaMqgUFxk dpkhQCB+Do2RHrDxLrcbGIOayT3hiO1HTiFwq7sAoZJFplFbtgy84nYqyvIYjMYk5d /js110otxNparE/PF8Ll46D+n48OYFRMmNdKs9oTRVI2ZGuuXT65PUqri0To12J408 goY4lmLH1Bvhw== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH v12 23/23] drm/bridge: synopsys: dw-dp: Retrain on hotplug with pre-enabled link To: "Sebastian Reichel" Cc: dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, robh@kernel.org, conor+dt@kernel.org In-Reply-To: <20261114-synopsys-dw-dp-improvements-v12-23-d42d3dc5bdd4@collabora.com> References: <20261114-synopsys-dw-dp-improvements-v12-0-d42d3dc5bdd4@collabora.com> <20261114-synopsys-dw-dp-improvements-v12-23-d42d3dc5bdd4@collabora.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Sat, 14 Nov 2026 05:25:57 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: sashiko-reviews@lists.linux.dev Sender: "dri-devel" X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 X-Archived-By: Thank you for your contribution! Sashiko AI review found 2 potential issues to consider: - [High] drm/bridge: dw-dp: dw_dp_hpd_work() retrains link before parsing sink DPCD - [Medium] drm/bridge: dw-dp: unlocked link state check and TOCTOU in dw_dp_link_retrain() -- commit ecb979561e6b36e93516c81e2368f1af68040e73 Author: Yury Smirnov drm/bridge: synopsys: dw-dp: Retrain on hotplug with pre-enabled link This commit retrains an already-enabled DisplayPort link on a long HPD pulse when a sink is detected before sending the DRM hotplug event. > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-dp.c b/drivers/gpu/drm/br= idge/synopsys/dw-dp.c > index bf3a53463394f..b245d62009139 100644 > --- a/drivers/gpu/drm/bridge/synopsys/dw-dp.c > +++ b/drivers/gpu/drm/bridge/synopsys/dw-dp.c > @@ -2394,6 +2394,12 @@ static void dw_dp_hpd_work(struct work_struct *wor= k) > dev_warn(dp->dev, "Retrain link failed\n"); > } > } else { > + if (dp->link.enabled && dw_dp_hpd_detect(dp)) { > + ret =3D dw_dp_link_retrain(dp); > + if (ret) > + dev_warn(dp->dev, "Retrain link failed\n"); > + } > + > drm_helper_hpd_irq_event(dp->bridge.dev); > } > } [Severity: High] Should dw_dp_link_retrain() run after drm_helper_hpd_irq_event() rather than before it? Connector detection in drm_helper_hpd_irq_event() invokes dw_dp_bridge_detect() -> dw_dp_hpd_detect_link() -> dw_dp_link_parse(), which calls dw_dp_link_reset() (zeroing link->rate, link->lanes, and link->caps) and then reads the sink's DPCD capabilities. If a previous unplug detection failed after dw_dp_link_reset() (for example, on a DP branch device or USB-C adapter when sink_count dropped to 0 and dw_dp_link_parse() returned -ENODEV), dp->link.rate and dp->link.lanes are still 0 when the sink is replugged. Calling dw_dp_link_retrain() first then runs dw_dp_phy_configure(dp, 0, 0, false), putting the PHY into P3 powerdown with all lanes disabled and failing link training before dw_dp_link_parse() has re-read the DPCD. Even when dp->link was not zeroed, retraining before drm_helper_hpd_irq_event() trains against stale DPCD capabilities without transitioning the replugged sink to DP_SET_POWER_D0 via drm_dp_link_power_up(), and the subsequent dw_dp_link_parse() call in drm_helper_hpd_irq_event() immediately resets dp->link and overwrites any downgraded link->rate. [Severity: Medium] Can dw_dp_link_retrain() race with a concurrent atomic disable and train a link whose PHY has already been powered off? dw_dp_hpd_work() checks dp->link.enabled and dw_dp_link_retrain() checks dw_dp_needs_link_retrain() before acquiring dev->mode_config.connection_mutex, and neither is rechecked after acquiring the lock: CPU0 (kworker) CPU1 (modeset) dw_dp_hpd_work() if (dp->link.enabled && ...) dw_dp_link_retrain() dw_dp_needs_link_retrain() dw_dp_bridge_atomic_disable() dw_dp_link_disable() dw_dp_phy_xmit_enable(dp, 0) phy_power_off(dp->phy) link->enabled =3D false drm_modeset_lock(&connection_mutex) dw_dp_link_train() dw_dp_phy_configure() <-- configures powered-off PHY Rechecking dp->link.enabled and dw_dp_needs_link_retrain() after locking connection_mutex would close this window. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261114-synopsys-d= w-dp-improvements-v12-0-d42d3dc5bdd4@collabora.com?part=3D23