[PATCH] drm/kmb: Avoid warnings on impossible plane_id

[Kees Cook]

KMB_MAX_PLANES is defined as 1, yet kmb_plane_atomic_disable() had code
for writing beyond 1. It is gated by a WARN_ON() that would skip it,
though, but under some compiler versions, poor Dead Code Elimination
wasn't optimizing away the unused switch cases, leading to array bounds
warnings when building with -Warray-bounds:

drivers/gpu/drm/kmb/kmb_plane.c:135:20: warning: array subscript 3 is above 
array bounds of 'struct layer_status[1]' [-Warray-bounds]
drivers/gpu/drm/kmb/kmb_plane.c:132:20: warning: array subscript 2 is above 
array bounds of 'struct layer_status[1]' [-Warray-bounds]
drivers/gpu/drm/kmb/kmb_plane.c:129:20: warning: array subscript 1 is above 
array bounds of 'struct layer_status[1]' [-Warray-bounds]

Instead, just remove the switch statement entirely and adjust the index
type to match the struct "id" member.

Cc: Anitha Chrisanthus <anitha.chrisant...@intel.com>
Cc: Edmund Dea <edmund.j....@intel.com>
Cc: David Airlie <airl...@linux.ie>
Cc: Daniel Vetter <dan...@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 drivers/gpu/drm/kmb/kmb_plane.c | 18 ++----------------
 1 file changed, 2 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/kmb/kmb_plane.c b/drivers/gpu/drm/kmb/kmb_plane.c
index ecee6782612d..3d46e756f2fe 100644
--- a/drivers/gpu/drm/kmb/kmb_plane.c
+++ b/drivers/gpu/drm/kmb/kmb_plane.c
@@ -113,7 +113,7 @@ static void kmb_plane_atomic_disable(struct drm_plane 
*plane,
                                     struct drm_atomic_state *state)
 {
        struct kmb_plane *kmb_plane = to_kmb_plane(plane);
-       int plane_id = kmb_plane->id;
+       unsigned char plane_id = kmb_plane->id;
        struct kmb_drm_private *kmb;
 
        kmb = to_kmb(plane->dev);
@@ -121,21 +121,7 @@ static void kmb_plane_atomic_disable(struct drm_plane 
*plane,
        if (WARN_ON(plane_id >= KMB_MAX_PLANES))
                return;
 
-       switch (plane_id) {
-       case LAYER_0:
-               kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL1_ENABLE;
-               break;
-       case LAYER_1:
-               kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL2_ENABLE;
-               break;
-       case LAYER_2:
-               kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL1_ENABLE;
-               break;
-       case LAYER_3:
-               kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL2_ENABLE;
-               break;
-       }
-
+       kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL1_ENABLE;
        kmb->plane_status[plane_id].disable = true;
 }
 
-- 
2.30.2