Re: [RFC PATCH 4/6] drm/msm/dsi: Use DSC slice(s) packet size to compute word count

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On 12/13/2022 3:22 PM, Marijn Suijten wrote:
According to downstream the value to use for WORD_COUNT is
bytes_per_pkt, which denotes the number of bytes in a packet based on
how many slices have been configured by the panel driver times the
width of a slice times the number of bytes per pixel.

The DSC panels seen thus far use one byte per pixel, only one slice
per packet, and a slice width of half the panel width leading to the
desired bytes_per_pkt+1 value to be equal to hdisplay/2+1.  This however
isn't the case anymore for panels that configure two slices per packet,
where the value should now be hdisplay+1.

Note that the aforementioned panel (on a Sony Xperia XZ3, sdm845) with
slice_count=1 has also been tested to successfully accept slice_count=2,
which would have shown corrupted output previously.

Fixes: 08802f515c3c ("drm/msm/dsi: Add support for DSC configuration")
Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>

Reviewed-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
---
  drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index b83cf70b1adb..0686c35a6fd4 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -989,7 +989,7 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
  		if (!msm_host->dsc)
  			wc = hdisplay * dsi_get_bpp(msm_host->format) / 8 + 1;
  		else
-			wc = mode->hdisplay / 2 + 1;
+			wc = msm_host->dsc->slice_chunk_size * msm_host->dsc->slice_count + 1;
dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_CTRL,
  			DSI_CMD_MDP_STREAM0_CTRL_WORD_COUNT(wc) |



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