Messages in this thread | | | Date | Tue, 9 May 2023 02:27:17 +0300 | Subject | Re: [PATCH 2/4] drm/msm/dsi: Fix compressed word count calculation | From | Dmitry Baryshkov <> |
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On 08/05/2023 23:09, Abhinav Kumar wrote: > > > On 5/3/2023 1:26 AM, Dmitry Baryshkov wrote: >> On 03/05/2023 04:19, Jessica Zhang wrote: >>> Currently, word count is calculated using slice_count. This is incorrect >>> as downstream uses slice per packet, which is different from >>> slice_count. >>> >>> Slice count represents the number of soft slices per interface, and its >>> value will not always match that of slice per packet. For example, it is >>> possible to have cases where there are multiple soft slices per >>> interface >>> but the panel specifies only one slice per packet. >>> >>> Thus, use the default value of one slice per packet and remove >>> slice_count >>> from the word count calculation. >>> >>> Fixes: bc6b6ff8135c ("drm/msm/dsi: Use DSC slice(s) packet size to >>> compute word count") >>> Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com> >>> --- >>> drivers/gpu/drm/msm/dsi/dsi_host.c | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c >>> b/drivers/gpu/drm/msm/dsi/dsi_host.c >>> index 35c69dbe5f6f..b0d448ffb078 100644 >>> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c >>> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c >>> @@ -996,7 +996,14 @@ 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 = msm_host->dsc->slice_chunk_size * >>> msm_host->dsc->slice_count + 1; >>> + /* >>> + * When DSC is enabled, WC = slice_chunk_size * >>> slice_per_packet + 1. >>> + * Currently, the driver only supports default value of >>> slice_per_packet = 1 >>> + * >>> + * TODO: Expand drm_panel struct to hold >>> slice_per_packet info >>> + * and adjust DSC math to account for >>> slice_per_packet. >> >> slice_per_packet is not a part of the standard DSC, so I'm not sure >> how that can be implemented. And definitely we should not care about >> the drm_panel here. It should be either a part of drm_dsc_config, or >> mipi_dsi_device. >> > > This is not correct. > > It is part of the DSI standard (not DSC standard). Please refer to > Figure 40 "One Line Containing One Packet with Data from One or More > Compressed Slices" and Figure 41 "One Line Containing More than One > Compressed Pixel Stream Packet".
I have reviewed section 8.8.24 and Annex D of the DSI standard.
It is not clear to me, if we can get away with always using slice_per_packet = 1. What is the DSI sink's difference between Fig. 40.(b) and Fig 41?
Are there are known panels that require slice_per_packet != 1? If so, we will have to implement support for such configurations.
> This has details about this. So I still stand by my point that this > should be in the drm_panel.
Note, the driver doesn't use drm_panel directly. So slices_per_packet should go to mipi_dsi_device instead (which in turn can be filled from e.g. drm_panel or from any other source).
> >>> + */ >>> + wc = msm_host->dsc->slice_chunk_size + 1; >>> dsi_write(msm_host, REG_DSI_CMD_MDP_STREAM0_CTRL, >>> DSI_CMD_MDP_STREAM0_CTRL_WORD_COUNT(wc) | >>> >>
-- With best wishes Dmitry
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