linux-kernel - Re: [PATCH 2/4] drm/msm/dsi: Fix compressed word count calculation

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Date:   Wed, 3 May 2023 11:26:42 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jessica Zhang <quic_jesszhan@...cinc.com>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Marijn Suijten <marijn.suijten@...ainline.org>
Cc:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] drm/msm/dsi: Fix compressed word count calculation

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@...cinc.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.

> +			 */
> +			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