[PATCH] drm: atmel-hlcdc: use a default gamma ramp if none is specified

[Peter Rosin <peda@axentia.se>]

At init and if the gamma_lut property is ever removed, the clut
registers must be programmed with a default gamma ramp instead of
being left in some unknown state.

Fixes: 364a7bf574eb ("drm: atmel-hlcdc: add support for 8-bit color lookup table mode")
Signed-off-by: Peter Rosin <peda@axentia.se>
---
 drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
index b5bd9b0..0ccd93c 100644
--- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
+++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
@@ -429,6 +429,14 @@ static void atmel_hlcdc_plane_update_format(struct atmel_hlcdc_plane *plane,
 				    ATMEL_HLCDC_LAYER_FORMAT_CFG, cfg);
 }
 
+static void atmel_hlcdc_default_gamma_ramp(struct atmel_hlcdc_layer *layer)
+{
+	int idx;
+
+	for (idx = 0; idx < ATMEL_HLCDC_CLUT_SIZE; idx++)
+		atmel_hlcdc_layer_write_clut(layer, idx, idx * 0x10101);
+}
+
 static void atmel_hlcdc_plane_update_clut(struct atmel_hlcdc_plane *plane)
 {
 	struct drm_crtc *crtc = plane->base.crtc;
@@ -438,9 +446,14 @@ static void atmel_hlcdc_plane_update_clut(struct atmel_hlcdc_plane *plane)
 	if (!crtc || !crtc->state)
 		return;
 
-	if (!crtc->state->color_mgmt_changed || !crtc->state->gamma_lut)
+	if (!crtc->state->color_mgmt_changed)
 		return;
 
+	if (!crtc->state->gamma_lut) {
+		atmel_hlcdc_default_gamma_ramp(&plane->layer);
+		return;
+	}
+
 	lut = (struct drm_color_lut *)crtc->state->gamma_lut->data;
 
 	for (idx = 0; idx < ATMEL_HLCDC_CLUT_SIZE; idx++, lut++) {
@@ -918,6 +931,8 @@ static int atmel_hlcdc_plane_init_properties(struct atmel_hlcdc_plane *plane,
 					    0x40040890);
 	}
 
+	atmel_hlcdc_default_gamma_ramp(&plane->layer);
+
 	return 0;
 }
 
-- 
2.1.4