drm/malidp: Fix writeback in NV12

When we want to writeback to memory in NV12 format we need to program
the RGB2YUV coefficients. Currently, we don't program the coefficients
and NV12 doesn't work at all.

This patchset fixes that by programming a sane default(bt709, limited
range) as rgb2yuv coefficients.

In the long run, probably we need to think of a way for userspace to
be able to program that, but for now I think this is better than not
working at all or not advertising NV12 as a supported format for
memwrite.

Changes since v1:
 - Write the rgb2yuv coefficients only once, since we don't change
   them at all, just write them the first time NV12 is programmed,
   suggested by Brian Starkey, here [1]

[1] https://lists.freedesktop.org/archives/dri-devel/2018-August/186819.html

Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

1 files changed, 21 insertions, 4 deletions

diff --git a/drivers/gpu/drm/arm/malidp_mw.c b/drivers/gpu/drm/arm/malidp_mw.c
index ba6ae66387c9..91472e5e0c8b 100644
--- a/drivers/gpu/drm/arm/malidp_mw.c
+++ b/drivers/gpu/drm/arm/malidp_mw.c
@@ -26,6 +26,8 @@ struct malidp_mw_connector_state {
 	s32 pitches[2];
 	u8 format;
 	u8 n_planes;
+	bool rgb2yuv_initialized;
+	const s16 *rgb2yuv_coeffs;
 };
 
 static int malidp_mw_connector_get_modes(struct drm_connector *connector)
@@ -84,7 +86,7 @@ static void malidp_mw_connector_destroy(struct drm_connector *connector)
 static struct drm_connector_state *
 malidp_mw_connector_duplicate_state(struct drm_connector *connector)
 {
-	struct malidp_mw_connector_state *mw_state;
+	struct malidp_mw_connector_state *mw_state, *mw_current_state;
 
 	if (WARN_ON(!connector->state))
 		return NULL;
@@ -93,7 +95,10 @@ malidp_mw_connector_duplicate_state(struct drm_connector *connector)
 	if (!mw_state)
 		return NULL;
 
-	/* No need to preserve any of our driver-local data */
+	mw_current_state = to_mw_state(connector->state);
+	mw_state->rgb2yuv_coeffs = mw_current_state->rgb2yuv_coeffs;
+	mw_state->rgb2yuv_initialized = mw_current_state->rgb2yuv_initialized;
+
 	__drm_atomic_helper_connector_duplicate_state(connector, &mw_state->base);
 
 	return &mw_state->base;
@@ -108,6 +113,13 @@ static const struct drm_connector_funcs malidp_mw_connector_funcs = {
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
 };
 
+static const s16 rgb2yuv_coeffs_bt709_limited[MALIDP_COLORADJ_NUM_COEFFS] = {
+	47,  157,   16,
+	-26,  -87,  112,
+	112, -102,  -10,
+	16,  128,  128
+};
+
 static int
 malidp_mw_encoder_atomic_check(struct drm_encoder *encoder,
 			       struct drm_crtc_state *crtc_state,
@@ -157,6 +169,9 @@ malidp_mw_encoder_atomic_check(struct drm_encoder *encoder,
 	}
 	mw_state->n_planes = n_planes;
 
+	if (fb->format->is_yuv)
+		mw_state->rgb2yuv_coeffs = rgb2yuv_coeffs_bt709_limited;
+
 	return 0;
 }
 
@@ -239,10 +254,12 @@ void malidp_mw_atomic_commit(struct drm_device *drm,
 
 		drm_writeback_queue_job(mw_conn, conn_state->writeback_job);
 		conn_state->writeback_job = NULL;
-
 		hwdev->hw->enable_memwrite(hwdev, mw_state->addrs,
 					   mw_state->pitches, mw_state->n_planes,
-					   fb->width, fb->height, mw_state->format);
+					   fb->width, fb->height, mw_state->format,
+					   !mw_state->rgb2yuv_initialized ?
+					   mw_state->rgb2yuv_coeffs : NULL);
+		mw_state->rgb2yuv_initialized = !!mw_state->rgb2yuv_coeffs;
 	} else {
 		DRM_DEV_DEBUG_DRIVER(drm->dev, "Disable memwrite\n");
 		hwdev->hw->disable_memwrite(hwdev);