linux-kernel - FAILED: Patch "drm/probe-helper: warn about negative .get_modes()" failed to apply to 4.19-stable tree

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Date: Wed, 27 Mar 2024 08:28:24 -0400
From: Sasha Levin <sashal@...nel.org>
To: stable@...r.kernel.org,
	jani.nikula@...el.com
Cc: Thomas Zimmermann <tzimmermann@...e.de>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: FAILED: Patch "drm/probe-helper: warn about negative .get_modes()" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@...r.kernel.org>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

>From 7af03e688792293ba33149fb8df619a8dff90e80 Mon Sep 17 00:00:00 2001
From: Jani Nikula <jani.nikula@...el.com>
Date: Fri, 8 Mar 2024 18:03:39 +0200
Subject: [PATCH] drm/probe-helper: warn about negative .get_modes()

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@...r.kernel.org
Acked-by: Thomas Zimmermann <tzimmermann@...e.de>
Link: https://patchwork.freedesktop.org/patch/msgid/50208c866facc33226a3c77b82bb96aeef8ef310.1709913674.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@...el.com>
---
 drivers/gpu/drm/drm_probe_helper.c       | 7 +++++++
 include/drm/drm_modeset_helper_vtables.h | 3 ++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 19ecb749704be..75f84753f6ee3 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -422,6 +422,13 @@ 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);
 
-- 
2.43.0