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Date:   Thu, 7 Dec 2023 01:28:59 +0800
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From:   bbaa <bbaa@bbaa.fun>
Subject: [Bug Report] drm/edid: drm_edid_override_connector_update returns a
 incorrect value
To:     maarten.lankhorst@linux.intel.com, mripard@kernel.org,
        tzimmermann@suse.de, airlied@gmail.com, daniel@ffwll.ch
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
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Hello everyone,

drm_edid_override_connector_update seem return a incorrect value.

drivers/gpu/drm/drm_edid.c (Linux 6.7-rc4)
   2294	/**
   2295	 * drm_edid_override_connector_update - add modes from override/firmware EDID
   2296	 * @connector: connector we're probing
   2297	 *
   2298	 * Add modes from the override/firmware EDID, if available. Only to be used from
   2299	 * drm_helper_probe_single_connector_modes() as a fallback for when DDC probe
   2300	 * failed during drm_get_edid() and caused the override/firmware EDID to be
   2301	 * skipped.
   2302	 *
   2303	 * Return: The number of modes added or 0 if we couldn't find any.
   2304	 */
   2305	int drm_edid_override_connector_update(struct drm_connector *connector)
   2306	{
   2307		const struct drm_edid *override;
   2308		int num_modes = 0;
   2309	
   2310		override = drm_edid_override_get(connector);
   2311		if (override) {
   2312			num_modes = drm_edid_connector_update(connector, override);
   2313	
   2314			drm_edid_free(override);
   2315	
   2316			drm_dbg_kms(connector->dev,
   2317				    "[CONNECTOR:%d:%s] adding %d modes via fallback override/firmware EDID\n",
   2318				    connector->base.id, connector->name, num_modes);
   2319		}
   2320	
   2321		return num_modes;
   2322	}
   2323	EXPORT_SYMBOL(drm_edid_override_connector_update);

The comment describes that it will return the number of modes added
However the function calls drm_edid_connector_update, will return 0 upon successful execution.

drivers/gpu/drm/drm_edid.c
   6813	/**
   6814	 * drm_edid_connector_update - Update connector information from EDID
   6815	 * @connector: Connector
   6816	 * @drm_edid: EDID
   6817	 *
   6818	 * Update the connector display info, ELD, HDR metadata, relevant properties,
   6819	 * etc. from the passed in EDID.
   6820	 *
   6821	 * If EDID is NULL, reset the information.
   6822	 *
   6823	 * Must be called before calling drm_edid_connector_add_modes().
   6824	 *
   6825	 * Return: 0 on success, negative error on errors.
   6826	 */
   6827	int drm_edid_connector_update(struct drm_connector *connector,
   6828				      const struct drm_edid *drm_edid)
   6829	{
   6830		update_display_info(connector, drm_edid);
   6831	
   6832		_drm_update_tile_info(connector, drm_edid);
   6833	
   6834		return _drm_edid_connector_property_update(connector, drm_edid);
   6835	}
   6836	EXPORT_SYMBOL(drm_edid_connector_update);

This will break the EDID override behavior on Nvidia graphics cards.

NVIDIA/open-gpu-kernel-modules:
kernel-open/nvidia-drm/nvidia-drm-connector.c:
   103  #if defined(NV_DRM_CONNECTOR_HAS_OVERRIDE_EDID)   104      if 
(connector->override_edid) {   105  #else   106      if 
(drm_edid_override_connector_update(connector) > 0) {   107  #endif 
   108          const struct drm_property_blob *edid = 
connector->edid_blob_ptr;   109 
drm_edid_override_connector_update(connector)  will return zero here.

regards,
bbaa