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[2001:14ba:a0db:1f00::8a5]) by smtp.gmail.com with ESMTPSA id h4-20020a05651211c400b004edc2a023ffsm146075lfr.36.2023.05.08.17.47.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 May 2023 17:47:50 -0700 (PDT) Message-ID: <9e9bbe10-8646-9443-06b2-fa6737d0c267@linaro.org> Date: Tue, 9 May 2023 03:47:50 +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> <4cf2e9ab-7e08-fb26-d924-8ea8141d9f58@linaro.org> From: Dmitry Baryshkov In-Reply-To: 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 09/05/2023 03:45, Abhinav Kumar wrote: > > > On 5/8/2023 4:27 PM, Dmitry Baryshkov wrote: >> 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? >> > > The difference is that in fig 40(b) there is only one packet of data > (check closely, there is only one header). > > In fig 41, there are multiple headers so its showing multiple packets. Yes, this is the description of the pictures. I mean what is the functional difference? > >> Are there are known panels that require slice_per_packet != 1? If so, >> we will have to implement support for such configurations. >> > > Unless explicitly requested by the panel, we can use 1. From the device > tree files of the panels we support downstream, I do see > qcom,mdss-dsc-slice-per-pkt set to 2 for some panels. I dont know > whether those panels will not work with 1. I really don't think any of > the DSC panels working with MSM were upstreamed. > > I think the one jessica will be posting (and merging) will be the first > and that works with 1. > > If there are other panels in the works which require 2 slice_per_pkt, I > would wait to first see them on the list and if they cannot work with 1 > slice_per_pkt, add support for that. If slice_per_pkt change is localized - touching only few lines in DSI or in msm_helpers. Otherwise we should consider having that from the beginning (but hardcoded to 1 for now). > >>> 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