[PATCH 1/2] drm/amd/display: avoid divide-by-zero in __is_lut_linear()

__is_lut_linear() computes the expected value of each entry with

	expected = i * MAX_DRM_LUT_VALUE / (size - 1);

If it is ever called with a single-entry LUT, size - 1 is zero and the
kernel takes a divide error (#DE). A LUT with fewer than two entries
cannot describe a linear mapping anyway, so return false early instead
of dividing by zero.

Fixes: 086247a4b2fb ("drm/amd/display: Use 4096 lut entries")
Cc: [email protected]
Signed-off-by: Harry Wentland <[email protected]>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
index 7b68c6846039..26e5c89375a5 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c
@@ -471,6 +471,12 @@ bool __is_lut_linear(const struct drm_color_lut *lut, uint32_t size)
 	uint32_t expected;
 	int delta;
 
+	/* A LUT with fewer than two entries can't be interpolated and would
+	 * divide by zero below (size - 1); it can't be treated as linear.
+	 */
+	if (size < 2)
+		return false;
+
 	for (i = 0; i < size; i++) {
 		/* All color values should equal */
 		if ((lut[i].red != lut[i].green) || (lut[i].green != lut[i].blue))
-- 
2.55.0