According to the comment this DPU register contains the bits per pixel
as a 6.4 fractional value, conveniently matching the contents of
bits_per_pixel in struct drm_dsc_config which also uses 4 fractional
bits. However, the downstream source this implementation was
copy-pasted from has its bpp field stored _without_ fractional part.
This makes the entire convoluted math obsolete as it is impossible to
pull those 4 fractional bits out of thin air, by somehow trying to reuse
the lowest 2 bits of a non-fractional bpp (lsb = bpp % 4??).
The rest of the code merely attempts to keep the integer part a multiple
of 4, which is rendered useless thanks to data |= dsc->bits_per_pixel <<
12; already filling up those bits anyway (but not on downstream).
Fixes: c110cfd1753e ("drm/msm/disp/dpu1: Add support for DSC")
Reviewed-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
Reviewed-by: Vinod Koul <vkoul@xxxxxxxxxx>
Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
---
drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c
index 46cc2afd2bb9..c63e6eef1ba6 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c
@@ -47,7 +47,7 @@ static void dpu_hw_dsc_config(struct dpu_hw_dsc *hw_dsc,
u32 initial_lines)
{
struct dpu_hw_blk_reg_map *c = &hw_dsc->hw;
- u32 data, lsb, bpp;
+ u32 data;
u32 slice_last_group_size;
u32 det_thresh_flatness;
bool is_cmd_mode = !(mode & DSC_MODE_VIDEO);
@@ -61,14 +61,7 @@ static void dpu_hw_dsc_config(struct dpu_hw_dsc *hw_dsc,
data = (initial_lines << 20);
data |= ((slice_last_group_size - 1) << 18);
/* bpp is 6.4 format, 4 LSBs bits are for fractional part */
- data |= dsc->bits_per_pixel << 12;
- lsb = dsc->bits_per_pixel % 4;
- bpp = dsc->bits_per_pixel / 4;
- bpp *= 4;
- bpp <<= 4;
- bpp |= lsb;
-
- data |= bpp << 8;
+ data |= (dsc->bits_per_pixel << 8);
data |= (dsc->block_pred_enable << 7);
data |= (dsc->line_buf_depth << 3);
data |= (dsc->simple_422 << 2);
--
2.38.0
