FAILED: patch "[PATCH] drm/fb-helper: defer setup when fbdev_probe() fails, not just" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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 <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 755c94d178b7e972bb766199d34e4ba4f63a89eb
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026101246-reason-finished-ac79@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 755c94d178b7e972bb766199d34e4ba4f63a89eb Mon Sep 17 00:00:00 2001
From: Nguyen Ngoc Thang <[email protected]>
Date: Sun, 27 Sep 2026 14:54:34 +0700
Subject: [PATCH] drm/fb-helper: defer setup when fbdev_probe() fails, not just
on -EAGAIN

__drm_fb_helper_initial_config_and_unlock() calls drm_client_modeset_probe() first, which already fills in each mode_set->mode/num_connectors for every connected output, and only afterwards calls drm_fb_helper_single_fb_probe() to create fb_helper->fb and wire it into those mode_sets via drm_setup_crtcs_fb().

If drm_fb_helper_single_fb_probe() fails with anything other than -EAGAIN (e.g. dev->driver->fbdev_probe() itself fails), the function bails out before drm_setup_crtcs_fb() runs and before setting fb_helper->deferred_setup. The client is left with mode_sets that have a mode and connectors but mode_set->fb == NULL, and nothing marks this fb_helper as needing a retry.

__drm_fb_helper_restore_fbdev_mode_unlocked() only skips committing when fb_helper->deferred_setup is set, so a later .restore() call (drm_lastclose() on process exit, in this report) commits the stale mode_set through drm_client_modeset_commit() -> drm_client_modeset_commit_atomic() -> __drm_atomic_helper_set_config(), which hits WARN_ON(!set->fb).

Mark fb_helper->deferred_setup on any drm_fb_helper_single_fb_probe() failure, not just -EAGAIN, so restore keeps skipping the commit until a later hotplug event successfully re-probes and re-populates mode_set->fb. The real error code is still returned to the caller unchanged.

index d4664ed468b2..0817b639b3fa 100644
@@ -1724,10 +1724,10 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper)
 
 	ret = drm_fb_helper_single_fb_probe(fb_helper);
 	if (ret < 0) {
-		if (ret == -EAGAIN) {
-			fb_helper->deferred_setup = true;
+		/* modesets are probed but fb_helper->fb isn't; defer restore too */
+		fb_helper->deferred_setup = true;
+		if (ret == -EAGAIN)
 			ret = 0;
-		}
 		mutex_unlock(&fb_helper->lock);
 
 		goto err_drm_fb_helper_release_info;

From: Nguyen Ngoc Thang <[email protected]>

[ Upstream commit 755c94d178b7e972bb766199d34e4ba4f63a89eb ]

__drm_fb_helper_initial_config_and_unlock() calls drm_client_modeset_probe() first, which already fills in each mode_set->mode/num_connectors for every connected output, and only afterwards calls drm_fb_helper_single_fb_probe() to create fb_helper->fb and wire it into those mode_sets via drm_setup_crtcs_fb().

If drm_fb_helper_single_fb_probe() fails with anything other than -EAGAIN (e.g. dev->driver->fbdev_probe() itself fails), the function bails out before drm_setup_crtcs_fb() runs and before setting fb_helper->deferred_setup. The client is left with mode_sets that have a mode and connectors but mode_set->fb == NULL, and nothing marks this fb_helper as needing a retry.

__drm_fb_helper_restore_fbdev_mode_unlocked() only skips committing when fb_helper->deferred_setup is set, so a later .restore() call (drm_lastclose() on process exit, in this report) commits the stale mode_set through drm_client_modeset_commit() -> drm_client_modeset_commit_atomic() -> __drm_atomic_helper_set_config(), which hits WARN_ON(!set->fb).

Mark fb_helper->deferred_setup on any drm_fb_helper_single_fb_probe() failure, not just -EAGAIN, so restore keeps skipping the commit until a later hotplug event successfully re-probes and re-populates mode_set->fb. The real error code is still returned to the caller unchanged.

---
 drivers/gpu/drm/drm_fb_helper.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

index bc265aa0f692b..acd90c22ea1fd 100644
@@ -1841,11 +1841,11 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper,
 	drm_client_modeset_probe(&fb_helper->client, width, height);
 	ret = drm_fb_helper_single_fb_probe(fb_helper, bpp_sel);
 	if (ret < 0) {
-		if (ret == -EAGAIN) {
-			fb_helper->preferred_bpp = bpp_sel;
-			fb_helper->deferred_setup = true;
+		fb_helper->preferred_bpp = bpp_sel;
+		/* modesets are probed but fb_helper->fb isn't; defer restore too */
+		fb_helper->deferred_setup = true;
+		if (ret == -EAGAIN)
 			ret = 0;
-		}
 		mutex_unlock(&fb_helper->lock);
 
 		return ret;

2.53.0