This is a note to let you know that I've just added the patch titled drm/msm/dpu1: Account for DSC's bits_per_pixel having 4 fractional bits to the 6.0-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-msm-dpu1-account-for-dsc-s-bits_per_pixel-having.patch and it can be found in the queue-6.0 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 71274d360a400694ffd7abea10047a059fdc2e5c Author: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx> Date: Wed Oct 26 20:28:23 2022 +0200 drm/msm/dpu1: Account for DSC's bits_per_pixel having 4 fractional bits [ Upstream commit d3c1a8663d0ddb74eaa51121ccbb8340739a12a8 ] 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") Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx> Reviewed-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> Reviewed-by: Vinod Koul <vkoul@xxxxxxxxxx> Patchwork: https://patchwork.freedesktop.org/patch/508946/ Link: https://lore.kernel.org/r/20221026182824.876933-10-marijn.suijten@xxxxxxxxxxxxxx Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> 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 f2ddcfb6f7ee..3662df698dae 100644 --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c @@ -42,7 +42,7 @@ 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); @@ -56,14 +56,7 @@ 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);