[PATCH v2 2/3] fbdev: pxafb: stop the smart-panel thread

[Matthias Goergens <matthias.goergens@gmail.com>]

pxafb_smart_init() starts the smart-panel refresh thread, but nothing
ever stops it: neither pxafb_remove() nor the probe error paths that
run after it.  The thread then keeps running on the devm-allocated
struct pxafb_info after it has been freed.

Stop the thread on removal, after pxafb_disable_controller(), which
waits for a refresh that only the thread signals, and on those probe
error paths.

A thread that has already exited must not be passed to kthread_stop()
unless the caller holds a reference to its task_struct (see the comment
above kthread_stop()).  This thread returns at once when the board
provides no smart_update callback, so check for the callback in
pxafb_smart_init() before starting the thread.  Probe now fails with
-EINVAL in that case, instead of succeeding with a smart panel that is
never refreshed.

This needs CONFIG_FB_PXA_SMARTPANEL and a board with a smart panel; I
found no in-tree board that provides smart_update.  Sashiko, the AI
review bot, pointed this out while reviewing a pxafb cleanup.  I have
no PXA hardware; this is build-tested only.

Link: https://lore.kernel.org/all/20260722081427.413EF1F000E9@smtp.kernel.org/
Fixes: 3c42a449107b ("pxafb: preliminary smart panel interface support")
Fixes: 9f17f2874834 ("[ARM] 5118/1: pxafb: add exit and remove handlers")
Signed-off-by: Matthias Goergens <matthias.goergens@gmail.com>
---
 drivers/video/fbdev/pxafb.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/video/fbdev/pxafb.c b/drivers/video/fbdev/pxafb.c
index 4f5c408eae56..b889a17e7304 100644
--- a/drivers/video/fbdev/pxafb.c
+++ b/drivers/video/fbdev/pxafb.c
@@ -1248,12 +1248,6 @@ static int pxafb_smart_thread(void *arg)
 	struct pxafb_info *fbi = arg;
 	struct pxafb_mach_info *inf = fbi->inf;
 
-	if (!inf->smart_update) {
-		pr_err("%s: not properly initialized, thread terminated\n",
-				__func__);
-		return -EINVAL;
-	}
-
 	pr_debug("%s(): task starting\n", __func__);
 
 	set_freezable();
@@ -1290,6 +1284,9 @@ static int pxafb_smart_init(struct pxafb_info *fbi)
 	init_completion(&fbi->command_done);
 	init_completion(&fbi->refresh_done);
 
+	if (!fbi->inf->smart_update)
+		return -EINVAL;
+
 	fbi->smart_thread = kthread_run(pxafb_smart_thread, fbi,
 					"lcd_refresh");
 	if (IS_ERR(fbi->smart_thread)) {
@@ -1299,8 +1296,15 @@ static int pxafb_smart_init(struct pxafb_info *fbi)
 
 	return 0;
 }
+
+static void pxafb_smart_exit(struct pxafb_info *fbi)
+{
+	if (!IS_ERR_OR_NULL(fbi->smart_thread))
+		kthread_stop(fbi->smart_thread);
+}
 #else
 static inline int pxafb_smart_init(struct pxafb_info *fbi) { return 0; }
+static inline void pxafb_smart_exit(struct pxafb_info *fbi) { }
 #endif /* CONFIG_FB_PXA_SMARTPANEL */
 
 static void setup_parallel_timing(struct pxafb_info *fbi,
@@ -2366,6 +2370,7 @@ static int pxafb_probe(struct platform_device *dev)
 	if (fbi->fb.cmap.len)
 		fb_dealloc_cmap(&fbi->fb.cmap);
 failed_free_mem:
+	pxafb_smart_exit(fbi);
 	free_pages_exact(fbi->video_mem, fbi->video_mem_size);
 failed_free_dma:
 	dma_free_coherent(&dev->dev, fbi->dma_buff_size,
@@ -2393,6 +2398,7 @@ static void pxafb_remove(struct platform_device *dev)
 	unregister_framebuffer(info);
 
 	pxafb_disable_controller(fbi);
+	pxafb_smart_exit(fbi);
 
 	if (fbi->fb.cmap.len)
 		fb_dealloc_cmap(&fbi->fb.cmap);
-- 
2.56.0