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Date:   Sun, 21 May 2023 03:32:56 +0300
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Subject: Re: [PATCH v3 5/5] drm/msm/dsi: Remove incorrect references to
 slice_count
Content-Language: en-GB
To:     Jessica Zhang <quic_jesszhan@quicinc.com>,
        Rob Clark <robdclark@gmail.com>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Marijn Suijten <marijn.suijten@somainline.org>
Cc:     Konrad Dybcio <konrad.dybcio@linaro.org>,
        linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org,
        freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org
References: <20230405-add-dsc-support-v3-0-6e1d35a206b3@quicinc.com>
 <20230405-add-dsc-support-v3-5-6e1d35a206b3@quicinc.com>
From:   Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
In-Reply-To: <20230405-add-dsc-support-v3-5-6e1d35a206b3@quicinc.com>
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Precedence: bulk

On 20/05/2023 00:17, Jessica Zhang wrote:
> Currently, slice_count is being used to calculate word count and
> pkt_per_line. In downstream, these values are calculated using slice per
> packet, which is not the same as slice_count.

I'd say the reference to downstream is not correct. We have seen cases 
where the vendor kernel contained errors. So it should be something like 
"Instead these values should be calculated using ...."

> 
> 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 aforementioned calculations.
> 
> Fixes: 08802f515c3c ("drm/msm/dsi: Add support for DSC configuration")
> 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 | 24 ++++++++++++++----------
>   1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index d04f8bbd707d..8c8858ee59ec 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -866,18 +866,15 @@ static void dsi_update_dsc_timing(struct msm_dsi_host *msm_host, bool is_cmd_mod
>   	 */
>   	slice_per_intf = msm_dsc_get_slices_per_intf(dsc, hdisplay);
>   
> -	/*
> -	 * If slice_count is greater than slice_per_intf
> -	 * then default to 1. This can happen during partial
> -	 * update.
> -	 */
> -	if (dsc->slice_count > slice_per_intf)
> -		dsc->slice_count = 1;
> -
>   	total_bytes_per_intf = dsc->slice_chunk_size * slice_per_intf;
>   
>   	eol_byte_num = total_bytes_per_intf % 3;
> -	pkt_per_line = slice_per_intf / dsc->slice_count;
> +
> +	/*
> +	 * Default to 1 slice_per_pkt, so pkt_per_line will be equal to
> +	 * slice per intf.
> +	 */
> +	pkt_per_line = slice_per_intf;
>   
>   	if (is_cmd_mode) /* packet data type */
>   		reg = DSI_COMMAND_COMPRESSION_MODE_CTRL_STREAM0_DATATYPE(MIPI_DSI_DCS_LONG_WRITE);
> @@ -1001,7 +998,14 @@ 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 mipi_dsi_device struct to hold slice_per_packet info
> +			 *       and adjust DSC math to account for slice_per_packet.
> +			 */
> +			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