Testing with the photometer shows that at least Raven Ridge DCN-1.0
does not achieve more than 10 bpc effective output precision with a
16 bpc unorm surface of type SURFACE_PIXEL_FORMAT_GRPH_ABGR16161616,
unless linebuffer depth is increased from LB_PIXEL_DEPTH_30BPP to
LB_PIXEL_DEPTH_36BPP. Otherwise precision gets truncated somewhere
to 10 bpc effective depth.

Strangely this increase was not needed on Polaris11 DCE-11.2 during
testing to get 12 bpc effective precision. It also is not needed for
fp16 framebuffers.

Tested on DCN-1.0 and DCE-11.2.

Signed-off-by: Mario Kleiner <mario.kleiner...@gmail.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_resource.c          | 7 +++++--
 drivers/gpu/drm/amd/display/dc/dce/dce_transform.c         | 6 ++++--
 drivers/gpu/drm/amd/display/dc/dce110/dce110_transform_v.c | 3 ++-
 drivers/gpu/drm/amd/display/dc/dcn10/dcn10_dpp.c           | 3 ++-
 drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c  | 2 +-
 drivers/gpu/drm/amd/display/dc/dcn20/dcn20_dpp.c           | 3 ++-
 drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c         | 2 +-
 drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c           | 3 ++-
 8 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c 
b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
index f1aed40b3124..51e91b546d69 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
@@ -1167,9 +1167,12 @@ bool resource_build_scaling_params(struct pipe_ctx 
*pipe_ctx)
 
        /**
         * Setting line buffer pixel depth to 24bpp yields banding
-        * on certain displays, such as the Sharp 4k
+        * on certain displays, such as the Sharp 4k. 36bpp is needed
+        * to support SURFACE_PIXEL_FORMAT_GRPH_ARGB16161616 and
+        * SURFACE_PIXEL_FORMAT_GRPH_ABGR16161616 with actual > 10 bpc
+        * precision on at least DCN display engines.
         */
-       pipe_ctx->plane_res.scl_data.lb_params.depth = LB_PIXEL_DEPTH_30BPP;
+       pipe_ctx->plane_res.scl_data.lb_params.depth = LB_PIXEL_DEPTH_36BPP;
        pipe_ctx->plane_res.scl_data.lb_params.alpha_en = 
plane_state->per_pixel_alpha;
 
        pipe_ctx->plane_res.scl_data.recout.x += timing->h_border_left;
diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_transform.c 
b/drivers/gpu/drm/amd/display/dc/dce/dce_transform.c
index 151dc7bf6d23..92b53a30d954 100644
--- a/drivers/gpu/drm/amd/display/dc/dce/dce_transform.c
+++ b/drivers/gpu/drm/amd/display/dc/dce/dce_transform.c
@@ -1647,7 +1647,8 @@ void dce_transform_construct(
        xfm_dce->lb_pixel_depth_supported =
                        LB_PIXEL_DEPTH_18BPP |
                        LB_PIXEL_DEPTH_24BPP |
-                       LB_PIXEL_DEPTH_30BPP;
+                       LB_PIXEL_DEPTH_30BPP |
+                       LB_PIXEL_DEPTH_36BPP;
 
        xfm_dce->lb_bits_per_entry = LB_BITS_PER_ENTRY;
        xfm_dce->lb_memory_size = LB_TOTAL_NUMBER_OF_ENTRIES; /*0x6B0*/
@@ -1675,7 +1676,8 @@ void dce60_transform_construct(
        xfm_dce->lb_pixel_depth_supported =
                        LB_PIXEL_DEPTH_18BPP |
                        LB_PIXEL_DEPTH_24BPP |
-                       LB_PIXEL_DEPTH_30BPP;
+                       LB_PIXEL_DEPTH_30BPP |
+                       LB_PIXEL_DEPTH_36BPP;
 
        xfm_dce->lb_bits_per_entry = LB_BITS_PER_ENTRY;
        xfm_dce->lb_memory_size = LB_TOTAL_NUMBER_OF_ENTRIES; /*0x6B0*/
diff --git a/drivers/gpu/drm/amd/display/dc/dce110/dce110_transform_v.c 
b/drivers/gpu/drm/amd/display/dc/dce110/dce110_transform_v.c
index 29438c6050db..45bca0db5e5e 100644
--- a/drivers/gpu/drm/amd/display/dc/dce110/dce110_transform_v.c
+++ b/drivers/gpu/drm/amd/display/dc/dce110/dce110_transform_v.c
@@ -708,7 +708,8 @@ bool dce110_transform_v_construct(
        xfm_dce->lb_pixel_depth_supported =
                        LB_PIXEL_DEPTH_18BPP |
                        LB_PIXEL_DEPTH_24BPP |
-                       LB_PIXEL_DEPTH_30BPP;
+                       LB_PIXEL_DEPTH_30BPP |
+                       LB_PIXEL_DEPTH_36BPP;
 
        xfm_dce->prescaler_on = true;
        xfm_dce->lb_bits_per_entry = LB_BITS_PER_ENTRY;
diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_dpp.c 
b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_dpp.c
index a77e7bd3b8d5..91fdfcd8a14e 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_dpp.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_dpp.c
@@ -568,7 +568,8 @@ void dpp1_construct(
        dpp->lb_pixel_depth_supported =
                LB_PIXEL_DEPTH_18BPP |
                LB_PIXEL_DEPTH_24BPP |
-               LB_PIXEL_DEPTH_30BPP;
+               LB_PIXEL_DEPTH_30BPP |
+               LB_PIXEL_DEPTH_36BPP;
 
        dpp->lb_bits_per_entry = LB_BITS_PER_ENTRY;
        dpp->lb_memory_size = LB_TOTAL_NUMBER_OF_ENTRIES; /*0x1404*/
diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c 
b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
index 89912bb5014f..25d198f60a1c 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
@@ -2470,7 +2470,7 @@ static void update_scaler(struct pipe_ctx *pipe_ctx)
                        pipe_ctx->plane_state->per_pixel_alpha && 
pipe_ctx->bottom_pipe;
 
        pipe_ctx->plane_res.scl_data.lb_params.alpha_en = per_pixel_alpha;
-       pipe_ctx->plane_res.scl_data.lb_params.depth = LB_PIXEL_DEPTH_30BPP;
+       pipe_ctx->plane_res.scl_data.lb_params.depth = LB_PIXEL_DEPTH_36BPP;
        /* scaler configuration */
        pipe_ctx->plane_res.dpp->funcs->dpp_set_scaler(
                        pipe_ctx->plane_res.dpp, &pipe_ctx->plane_res.scl_data);
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_dpp.c 
b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_dpp.c
index f2f44ddf522a..a9e420c7d75a 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_dpp.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_dpp.c
@@ -432,7 +432,8 @@ bool dpp2_construct(
        dpp->lb_pixel_depth_supported =
                LB_PIXEL_DEPTH_18BPP |
                LB_PIXEL_DEPTH_24BPP |
-               LB_PIXEL_DEPTH_30BPP;
+               LB_PIXEL_DEPTH_30BPP |
+               LB_PIXEL_DEPTH_36BPP;
 
        dpp->lb_bits_per_entry = LB_BITS_PER_ENTRY;
        dpp->lb_memory_size = LB_TOTAL_NUMBER_OF_ENTRIES; /*0x1404*/
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c 
b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
index 0726fb435e2a..cd924f4688e1 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
@@ -1467,7 +1467,7 @@ static void dcn20_update_dchubp_dpp(
                        plane_state->update_flags.bits.per_pixel_alpha_change ||
                        pipe_ctx->stream->update_flags.bits.scaling) {
                pipe_ctx->plane_res.scl_data.lb_params.alpha_en = 
pipe_ctx->plane_state->per_pixel_alpha;
-               ASSERT(pipe_ctx->plane_res.scl_data.lb_params.depth == 
LB_PIXEL_DEPTH_30BPP);
+               ASSERT(pipe_ctx->plane_res.scl_data.lb_params.depth == 
LB_PIXEL_DEPTH_36BPP);
                /* scaler configuration */
                pipe_ctx->plane_res.dpp->funcs->dpp_set_scaler(
                                pipe_ctx->plane_res.dpp, 
&pipe_ctx->plane_res.scl_data);
diff --git a/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c 
b/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c
index 0bc5c5eba7af..9c8138e52ded 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_dpp.c
@@ -1443,7 +1443,8 @@ bool dpp3_construct(
        dpp->lb_pixel_depth_supported =
                LB_PIXEL_DEPTH_18BPP |
                LB_PIXEL_DEPTH_24BPP |
-               LB_PIXEL_DEPTH_30BPP;
+               LB_PIXEL_DEPTH_30BPP |
+               LB_PIXEL_DEPTH_36BPP;
 
        dpp->lb_bits_per_entry = LB_BITS_PER_ENTRY;
        dpp->lb_memory_size = LB_TOTAL_NUMBER_OF_ENTRIES; /*0x1404*/
-- 
2.25.1

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