Patch "drm/probe-helper: warn about negative .get_modes()" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    drm/probe-helper: warn about negative .get_modes()

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-probe-helper-warn-about-negative-.get_modes.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6f9f5ffed661a3299b7883f12f6c0a92b6dccfa5
Author: Jani Nikula <jani.nikula@xxxxxxxxx>
Date:   Fri Mar 8 18:03:39 2024 +0200

    drm/probe-helper: warn about negative .get_modes()
    
    [ Upstream commit 7af03e688792293ba33149fb8df619a8dff90e80 ]
    
    The .get_modes() callback is supposed to return the number of modes,
    never a negative error code. If a negative value is returned, it'll just
    be interpreted as a negative count, and added to previous calculations.
    
    Document the rules, but handle the negative values gracefully with an
    error message.
    
    Cc: stable@xxxxxxxxxxxxxxx
    Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
    Link: https://patchwork.freedesktop.org/patch/msgid/50208c866facc33226a3c77b82bb96aeef8ef310.1709913674.git.jani.nikula@xxxxxxxxx
    Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 23b4e9a3361d8..744cde9db246b 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -419,6 +419,13 @@ static int drm_helper_probe_get_modes(struct drm_connector *connector)
 
 	count = connector_funcs->get_modes(connector);
 
+	/* The .get_modes() callback should not return negative values. */
+	if (count < 0) {
+		drm_err(connector->dev, ".get_modes() returned %pe\n",
+			ERR_PTR(count));
+		count = 0;
+	}
+
 	/*
 	 * Fallback for when DDC probe failed in drm_get_edid() and thus skipped
 	 * override/firmware EDID.
diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 881b03e4dc288..9ed42469540eb 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -898,7 +898,8 @@ struct drm_connector_helper_funcs {
 	 *
 	 * RETURNS:
 	 *
-	 * The number of modes added by calling drm_mode_probed_add().
+	 * The number of modes added by calling drm_mode_probed_add(). Return 0
+	 * on failures (no modes) instead of negative error codes.
 	 */
 	int (*get_modes)(struct drm_connector *connector);