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 explicitly canceled during connector cleanup, risking a Use-After-Free. - [High] The SCDC configuration helpers attempt to execute I2C transfers without verifying that `connector->ddc` is not NULL, leading to a NULL pointer dereference. - [High] The newly added HDMI scrambling helpers invoke sleeping functions in atomic context. - [Medium] The SCDC scrambling monitor delayed work fails to reschedule itself under normal conditions or upon recovery failure, breaking the intended periodic polling. --
commit 8b2652a7b68d13a84c5a135061f33fe6fdd00be1 Author: Cristian Ciocaltea <[email protected]> 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 = drm_scdc_set_high_tmds_clock_ratio(connector, true); > + if (!done) > + return -EIO; > + > + done = 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 = &connector->hdmi; > + struct drm_device *dev = 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 = drm_scdc_monitor_scrambler; > + WRITE_ONCE(hdmi->scrambler_enabled, true); > + > + ret = drm_scdc_try_scrambling_setup(connector); > + if (!ret) > + ret = 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 *connector) > +{ > + struct drm_connector_hdmi *hdmi = &connector->hdmi; > + struct drm_device *dev = 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 > plugged, > + struct drm_modeset_acquire_ctx *ctx) > +{ > + struct drm_connector_hdmi *hdmi = &connector->hdmi; > + struct drm_device *dev = 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 = 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. -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=7
