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 643B6C43458 for ; Thu, 2 Jul 2026 15:13:08 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id B52E410F43F; Thu, 2 Jul 2026 15:13:07 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="QjVqHHqy"; dkim-atps=neutral Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by gabe.freedesktop.org (Postfix) with ESMTPS id F096210F43F for ; Thu, 2 Jul 2026 15:13:05 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 4E331601C6; Thu, 2 Jul 2026 15:13:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E286F1F000E9; Thu, 2 Jul 2026 15:13:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783005185; bh=QWtEhBNlVU1TTnwCgwDWQ9MeEzmT6op8hGgRZtwULtw=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=QjVqHHqyGb8ZNrfXn6VeTcDMWtz3thdWXSmaLB6kPneotg3RPno7/R+O6MkXWxtXd 0hJfbLaHCj2jS5fIjimJWM99Rlf4F+Xc+ukLHFNXyfpcwCDgphBVi6HwGxpzCSZAa3 OYgO46hQ486sc6JdLcQCVNenU2gXXwzvK/NI0DhXclUsTLdm9HxodP4/NF+YziVoRt KdEKVnubZ13vqliEA/INHbAdXngu/iKYbvSo/vxxTxuAiRfvodJUYfDcARhGj+Brj7 VgkM+MGLuQ1Api93S0tGywtOOuK1yppdiZDhX9M91U2Qir6hiVIE6NjG58D/5118UR 2/Zb+MLB38uEg== From: sashiko-bot@kernel.org Subject: Re: [PATCH v8 07/39] drm/display: hdmi: Add HDMI 2.0 scrambling management helpers To: "Cristian Ciocaltea" Cc: dri-devel@lists.freedesktop.org In-Reply-To: <20260702-dw-hdmi-qp-scramb-v8-7-d79890d00b6a@collabora.com> References: <20260702-dw-hdmi-qp-scramb-v8-0-d79890d00b6a@collabora.com> <20260702-dw-hdmi-qp-scramb-v8-7-d79890d00b6a@collabora.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Thu, 02 Jul 2026 15:13:04 +0000 Message-Id: <20260702151304.E286F1F000E9@smtp.kernel.org> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: sashiko-reviews@lists.linux.dev Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Thank you for your contribution! Sashiko AI review found 4 potential issue(= s) to consider: - [High] The `scdc_work` delayed work item is initialized but never explici= tly canceled during connector cleanup, risking a Use-After-Free. - [High] The SCDC configuration helpers attempt to execute I2C transfers wi= thout verifying that `connector->ddc` is not NULL, leading to a NULL pointe= r dereference. - [High] The newly added HDMI scrambling helpers invoke sleeping functions = in atomic context. - [Medium] The SCDC scrambling monitor delayed work fails to reschedule its= elf under normal conditions or upon recovery failure, breaking the intended= periodic polling. -- commit 8b2652a7b68d13a84c5a135061f33fe6fdd00be1 Author: Cristian Ciocaltea drm/display: hdmi: Add HDMI 2.0 scrambling management helpers Add helpers to manage the full lifecycle of HDMI 2.0 SCDC scrambling on both source and sink sides: - drm_hdmi_mode_needs_scrambling(): checks whether a mode, bits per component and output format combination requires scrambling, which is needed when the resulting TMDS character rate exceeds the HDMI 1.3 maximum of 340 MHz - drm_connector_hdmi_enable_scrambling(): configures SCDC scrambling and high TMDS clock ratio and starts a periodic work item that monitors the sink's SCDC scrambling status, retrying setup when the sink loses state - drm_connector_hdmi_disable_scrambling(): tears down scrambling on both sides and cancels the monitoring work - drm_connector_hdmi_sync_scdc(): triggers a CRTC reset on reconnection to restore SCDC state lost during sink disconnects within an active display pipeline > diff --git a/drivers/gpu/drm/display/drm_hdmi_helper.c b/drivers/gpu/drm/= display/drm_hdmi_helper.c > index 5cb0b033b1713..7c96cccf683d4 100644 > --- a/drivers/gpu/drm/display/drm_hdmi_helper.c > +++ b/drivers/gpu/drm/display/drm_hdmi_helper.c [ ... ] > +static int drm_scdc_try_scrambling_setup(struct drm_connector *connector) > +{ > + bool done; > + > + done =3D drm_scdc_set_high_tmds_clock_ratio(connector, true); > + if (!done) > + return -EIO; > + > + done =3D drm_scdc_set_scrambling(connector, true); > + if (!done) > + return -EIO; > + > + if (READ_ONCE(connector->hdmi.scrambler_enabled)) > + schedule_delayed_work(&connector->hdmi.scdc_work, > + msecs_to_jiffies(DRM_HDMI_SCDC_POLL_DELAY_MS)); > + > + return 0; > +} > + > +static void drm_scdc_monitor_scrambler(struct drm_connector *connector) > +{ > + if (READ_ONCE(connector->hdmi.scrambler_enabled) && > + !drm_scdc_get_scrambling_status(connector)) > + drm_scdc_try_scrambling_setup(connector); > +} [Severity: Medium] Does this periodic monitoring loop stop unintentionally? If drm_scdc_get_scrambling_status() returns true to indicate normal status, or if drm_scdc_try_scrambling_setup() fails and returns early without rescheduling, the delayed work is never scheduled again. This appears to break the intended periodic polling loop in both the success and persistent-failure paths. [Severity: High] Is the scdc_work delayed work item explicitly cancelled when the connector is destroyed? If a connector is destroyed abruptly while the work is pending, it seems drm_connector_cleanup() will clear the connector structure using memset without first calling cancel_delayed_work_sync(&connector->hdmi.scdc_work). Could this leave a corrupted entry in the timer list, leading to a panic when the timer fires? [ ... ] > +int drm_connector_hdmi_enable_scrambling(struct drm_connector *connector, > + const struct drm_connector_state *conn_state) > +{ > + struct drm_connector_hdmi *hdmi =3D &connector->hdmi; > + struct drm_device *dev =3D connector->dev; > + int ret; > + > + if (!conn_state) > + return -EINVAL; > + > + if (!conn_state->hdmi.scrambler_needed) > + return 0; > + > + if (!hdmi->scrambler_supported) { > + drm_dbg_kms(dev, "Source doesn't support scrambling.\n"); > + return -EINVAL; > + } > + > + if (!drm_scdc_sink_supports_scrambling(connector)) { > + drm_dbg_kms(dev, "Sink doesn't support scrambling.\n"); > + return -EINVAL; > + } [Severity: High] Is it possible for connector->ddc to be NULL here? If an EDID advertising SCDC is forced on a connector that physically lacks an I2C DDC bus, drm_scdc_sink_supports_scrambling() might pass because it only checks the EDID capabilities. This would lead to a NULL pointer dereference when I2C transfers are attempted later in the function. > + > + drm_dbg_kms(dev, "Enabling scrambling\n"); > + > + hdmi->scdc_cb =3D drm_scdc_monitor_scrambler; > + WRITE_ONCE(hdmi->scrambler_enabled, true); > + > + ret =3D drm_scdc_try_scrambling_setup(connector); > + if (!ret) > + ret =3D hdmi->funcs->scrambler_enable(connector); > + > + if (ret) { > + WRITE_ONCE(hdmi->scrambler_enabled, false); > + cancel_delayed_work_sync(&hdmi->scdc_work); [Severity: High] Are sleeping functions being called from an atomic context here? These scrambling helpers appear to be invoked from encoder and bridge atomic enable/disable paths where sleeping is strictly forbidden. However, drm_scdc_try_scrambling_setup() indirectly uses usleep_range(), and cancel_delayed_work_sync() can also sleep. Could this cause deadlocks or system instability during modesets? [ ... ] > +int drm_connector_hdmi_disable_scrambling(struct drm_connector *connecto= r) > +{ > + struct drm_connector_hdmi *hdmi =3D &connector->hdmi; > + struct drm_device *dev =3D connector->dev; > + > + if (!READ_ONCE(hdmi->scrambler_enabled)) > + return 0; > + > + drm_dbg_kms(dev, "Disabling scrambling\n"); > + > + WRITE_ONCE(hdmi->scrambler_enabled, false); > + cancel_delayed_work_sync(&hdmi->scdc_work); [Severity: High] Could this cancel_delayed_work_sync() call sleep in an atomic disable path? Like the enable path, this disable helper uses a synchronization function that can sleep. This violates the requirement that atomic disable callbacks must not sleep. [ ... ] > +int drm_connector_hdmi_sync_scdc(struct drm_connector *connector, bool p= lugged, > + struct drm_modeset_acquire_ctx *ctx) > +{ > + struct drm_connector_hdmi *hdmi =3D &connector->hdmi; > + struct drm_device *dev =3D connector->dev; > + struct drm_connector_state *conn_state; > + struct drm_crtc *crtc; > + u8 config; > + int ret; [ ... ] > + if (!drm_scdc_sink_supports_scrambling(connector)) > + return 0; > + > + if (conn_state->commit && > + !try_wait_for_completion(&conn_state->commit->hw_done)) > + return 0; > + > + ret =3D drm_scdc_readb(connector->ddc, SCDC_TMDS_CONFIG, &config); [Severity: High] Does this code need to verify connector->ddc before using it? Similar to the enable path, if the connector lacks a physical I2C bus but SCDC is supported by the EDID, reading from connector->ddc here without a NULL check will result in a kernel panic. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260702-dw-hdmi-qp= -scramb-v8-0-d79890d00b6a@collabora.com?part=3D7