media: vivid: work around high stack usage with clang

Building a KASAN-enabled kernel with clang ends up in a case where too
much is inlined into vivid_thread_vid_cap() and the stack usage grows
a lot, possibly when the register allocation fails to produce efficient
code and spills a lot of temporaries to the stack. This uses more
than twice the amount of stack than the sum of the individual functions
when they are not inlined:

drivers/media/platform/vivid/vivid-kthread-cap.c:766:12: error: stack frame size of 2208 bytes in function 'vivid_thread_vid_cap' [-Werror,-Wframe-larger-than=]

Marking two of the key functions in here as 'noinline_for_stack' avoids
the pathological case in clang without any apparent downside for gcc.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/platform/vivid/vivid-kthread-cap.c

@@ -232,8 +232,8 @@ static void *plane_vaddr(struct tpg_data *tpg, struct vivid_buffer *buf,
 	return vbuf;
 }
 
-static int vivid_copy_buffer(struct vivid_dev *dev, unsigned p, u8 *vcapbuf,
-		struct vivid_buffer *vid_cap_buf)
+static noinline_for_stack int vivid_copy_buffer(struct vivid_dev *dev, unsigned p,
+		u8 *vcapbuf, struct vivid_buffer *vid_cap_buf)
 {
 	bool blank = dev->must_blank[vid_cap_buf->vb.vb2_buf.index];
 	struct tpg_data *tpg = &dev->tpg;
@@ -672,7 +672,8 @@ static void vivid_cap_update_frame_period(struct vivid_dev *dev)
 	dev->cap_frame_period = f_period;
 }
 
-static void vivid_thread_vid_cap_tick(struct vivid_dev *dev, int dropped_bufs)
+static noinline_for_stack void vivid_thread_vid_cap_tick(struct vivid_dev *dev,
+							 int dropped_bufs)
 {
 	struct vivid_buffer *vid_cap_buf = NULL;
 	struct vivid_buffer *vbi_cap_buf = NULL;