[PATCH resend] drm/armada: Fix off-by-one error in armada_overlay_get_property()

[PATCH resend] drm/armada: Fix off-by-one error in armada_overlay_get_property()

[Geert Uytterhoeven]

As ffs() returns one more than the index of the first bit set (zero
means no bits set), the color key mode value is shifted one position too
much.

Fix this by using FIELD_GET() instead.

Fixes: c96103b6c49ff9a8 ("drm/armada: move colorkey properties into overlay plane state")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Compile-tested only.
---
 drivers/gpu/drm/armada/armada_overlay.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/armada/armada_overlay.c b/drivers/gpu/drm/armada/armada_overlay.c
index f21eb8fb76d87285..3b9bd8ecda137f6d 100644
--- a/drivers/gpu/drm/armada/armada_overlay.c
+++ b/drivers/gpu/drm/armada/armada_overlay.c
@@ -4,6 +4,8 @@
  *  Rewritten from the dovefb driver, and Armada510 manuals.
  */
 
+#include <linux/bitfield.h>
+
 #include <drm/armada_drm.h>
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
@@ -445,8 +447,8 @@ static int armada_overlay_get_property(struct drm_plane *plane,
 			     drm_to_overlay_state(state)->colorkey_ug,
 			     drm_to_overlay_state(state)->colorkey_vb, 0);
 	} else if (property == priv->colorkey_mode_prop) {
-		*val = (drm_to_overlay_state(state)->colorkey_mode &
-			CFG_CKMODE_MASK) >> ffs(CFG_CKMODE_MASK);
+		*val = FIELD_GET(CFG_CKMODE_MASK,
+				 drm_to_overlay_state(state)->colorkey_mode);
 	} else if (property == priv->brightness_prop) {
 		*val = drm_to_overlay_state(state)->brightness + 256;
 	} else if (property == priv->contrast_prop) {
-- 
2.25.1

Re: [PATCH resend] drm/armada: Fix off-by-one error in armada_overlay_get_property()

[Russell King (Oracle)]

On Mon, Nov 21, 2022 at 04:43:14PM +0100, Geert Uytterhoeven wrote:
> As ffs() returns one more than the index of the first bit set (zero
> means no bits set), the color key mode value is shifted one position too
> much.
> 
> Fix this by using FIELD_GET() instead.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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