[PATCH 2/4] drm/sun4i: layers: Fix VI buffer address for clipped offsets

[Chen-Yu Tsai <wenst@chromium.org>]

Commit 79ac1c945ab8 ("drm/sun4i: layers: Use drm_fb_dma_get_gem_addr() to
get display memory") dropped the code to calculate the framebuffer's DMA
address in favor of drm_fb_dma_get_gem_addr().

This turned out to be wrong in a couple ways. The hardware is programmed
with clipped dimensions, so it needs the buffer address to start at the
clipped boundary. Moving to the helper negated the clipping. Also, when
clipping on the left, the buffer address needs to start at the first
pixel in the sub-sampling group even for the luma plane. The hardware
handles the interpolation internally.

Switch to the new drm_fb_dma_get_gem_clipped_addr(), which provides the
buffer address starting at the clipped boundary. Calculate the intra-group
offset and adjust the luma plane buffer address so that it points to the
start of the sub-sampling group.

Fixes: 79ac1c945ab8 ("drm/sun4i: layers: Use drm_fb_dma_get_gem_addr() to get display memory")
Cc: <stable@vger.kernel.org> # v7.1+, needs drm_fb_dma_get_gem_clipped_addr()
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
This is an alternative to Jernej's original revert:
https://lore.kernel.org/all/3980ea1aeb3f7fe8b4700e36560deeba3d050664.1785772659.git.jernej.skrabec@gmail.com/
---
 drivers/gpu/drm/sun4i/sun8i_ui_layer.c |  2 +-
 drivers/gpu/drm/sun4i/sun8i_vi_layer.c | 16 +++++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun8i_ui_layer.c b/drivers/gpu/drm/sun4i/sun8i_ui_layer.c
index bad102134726..530efae7e13c 100644
--- a/drivers/gpu/drm/sun4i/sun8i_ui_layer.c
+++ b/drivers/gpu/drm/sun4i/sun8i_ui_layer.c
@@ -130,7 +130,7 @@ static void sun8i_ui_layer_update_buffer(struct sun8i_layer *layer,
 	ch_base = sun8i_channel_base(layer);
 
 	/* Get the start of the displayed memory */
-	dma_addr = drm_fb_dma_get_gem_addr(fb, state, 0);
+	dma_addr = drm_fb_dma_get_gem_clipped_addr(fb, state, 0);
 
 	/* Set the line width */
 	DRM_DEBUG_DRIVER("Layer line width: %d bytes\n", fb->pitches[0]);
diff --git a/drivers/gpu/drm/sun4i/sun8i_vi_layer.c b/drivers/gpu/drm/sun4i/sun8i_vi_layer.c
index 2e9cda45c04e..7a1d5f1db037 100644
--- a/drivers/gpu/drm/sun4i/sun8i_vi_layer.c
+++ b/drivers/gpu/drm/sun4i/sun8i_vi_layer.c
@@ -205,7 +205,21 @@ static void sun8i_vi_layer_update_buffer(struct sun8i_layer *layer,
 
 	for (i = 0; i < format->num_planes; i++) {
 		/* Get the start of the displayed memory */
-		dma_addr = drm_fb_dma_get_gem_addr(fb, state, i);
+		dma_addr = drm_fb_dma_get_gem_clipped_addr(fb, state, i);
+
+		/*
+		 * The mixer can handle odd offsets into sub-sampled YUV
+		 * planes, but needs the address of the first pixel in each
+		 * sub-sampled block. Adjust the luma buffer address backwards.
+		 */
+		if (i == 0) {
+			u32 x_diff, y_diff;
+
+			x_diff = (state->src.x1 >> 16) & (format->hsub - 1);
+			y_diff = (state->src.y1 >> 16) & (format->vsub - 1);
+			dma_addr -= y_diff * fb->pitches[i];
+			dma_addr -= x_diff * format->cpp[i];
+		}
 
 		/* Set the line width */
 		DRM_DEBUG_DRIVER("Layer %d. line width: %d bytes\n",
-- 
2.55.0.979.g7e5102b832-goog