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[2001:14ba:a0db:1f00::8a5]) by smtp.gmail.com with ESMTPSA id z4-20020a2e7e04000000b002a8e758f669sm1322546ljc.27.2023.05.08.16.27.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 May 2023 16:27:17 -0700 (PDT) Message-ID: <4cf2e9ab-7e08-fb26-d924-8ea8141d9f58@linaro.org> Date: Tue, 9 May 2023 02:27:17 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH 2/4] drm/msm/dsi: Fix compressed word count calculation Content-Language: en-GB To: Abhinav Kumar , Jessica Zhang , Rob Clark , Sean Paul , David Airlie , Daniel Vetter , Marijn Suijten Cc: Konrad Dybcio , 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-v1-0-6bc6f03ae735@quicinc.com> <20230405-add-dsc-support-v1-2-6bc6f03ae735@quicinc.com> <32d473a6-f7a5-9aa6-85cf-0f77f1c071ce@quicinc.com> From: Dmitry Baryshkov In-Reply-To: <32d473a6-f7a5-9aa6-85cf-0f77f1c071ce@quicinc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >>> --- >>>   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