On Mon, 27 Feb 2023 at 01:49, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote: > > > > On 2/26/2023 5:09 AM, Dmitry Baryshkov wrote: > > On 26/02/2023 02:47, Abhinav Kumar wrote: > >> Hi Dmitry > >> > >> On 2/25/2023 7:23 AM, Dmitry Baryshkov wrote: > >>> On 25/02/2023 02:36, Abhinav Kumar wrote: > >>>> > >>>> > >>>> On 2/24/2023 3:53 PM, Dmitry Baryshkov wrote: > >>>>> On Sat, 25 Feb 2023 at 00:26, Abhinav Kumar > >>>>> <quic_abhinavk@xxxxxxxxxxx> wrote: > >>>>>> On 2/24/2023 1:36 PM, Dmitry Baryshkov wrote: > >>>>>>> 24 февраля 2023 г. 23:23:03 GMT+02:00, Abhinav Kumar > >>>>>>> <quic_abhinavk@xxxxxxxxxxx> пишет: > >>>>>>>> On 2/24/2023 1:13 PM, Dmitry Baryshkov wrote: > >>>>>>>>> On 24/02/2023 21:40, Kuogee Hsieh wrote: > >>>>>>>>>> Add DSC helper functions based on DSC configuration profiles > >>>>>>>>>> to produce > >>>>>>>>>> DSC related runtime parameters through both table look up and > >>>>>>>>>> runtime > >>>>>>>>>> calculation to support DSC on DPU. > >>>>>>>>>> > >>>>>>>>>> There are 6 different DSC configuration profiles are supported > >>>>>>>>>> currently. > >>>>>>>>>> DSC configuration profiles are differiented by 5 keys, DSC > >>>>>>>>>> version (V1.1), > >>>>>>>>>> chroma (444/422/420), colorspace (RGB/YUV), bpc(8/10), > >>>>>>>>>> bpp (6/7/7.5/8/9/10/12/15) and SCR (0/1). > >>>>>>>>>> > >>>>>>>>>> Only DSC version V1.1 added and V1.2 will be added later. > >>>>>>>>> > >>>>>>>>> These helpers should go to > >>>>>>>>> drivers/gpu/drm/display/drm_dsc_helper.c > >>>>>>>>> Also please check that they can be used for i915 or for amdgpu > >>>>>>>>> (ideally for both of them). > >>>>>>>>> > >>>>>>>> > >>>>>>>> No, it cannot. So each DSC encoder parameter is calculated based > >>>>>>>> on the HW core which is being used. > >>>>>>>> > >>>>>>>> They all get packed to the same DSC structure which is the > >>>>>>>> struct drm_dsc_config but the way the parameters are computed is > >>>>>>>> specific to the HW. > >>>>>>>> > >>>>>>>> This DPU file helper still uses the drm_dsc_helper's > >>>>>>>> drm_dsc_compute_rc_parameters() like all other vendors do but > >>>>>>>> the parameters themselves are very HW specific and belong to > >>>>>>>> each vendor's dir. > >>>>>>>> > >>>>>>>> This is not unique to MSM. > >>>>>>>> > >>>>>>>> Lets take a few other examples: > >>>>>>>> > >>>>>>>> AMD: > >>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dml/dsc/rc_calc_fpu.c#L165 > >>>>>>>> > >>>>>>>> > >>>>>>>> i915: > >>>>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L379 > >>>>>>>> > >>>>>>> > >>>>>>> I checked several values here. Intel driver defines more bpc/bpp > >>>>>>> combinations, but the ones which are defined in intel_vdsc and in > >>>>>>> this patch seem to match. If there are major differences there, > >>>>>>> please point me to the exact case. > >>>>>>> > >>>>>>> I remember that AMD driver might have different values. > >>>>>>> > >>>>>> > >>>>>> Some values in the rc_params table do match. But the > >>>>>> rc_buf_thresh[] doesnt. > >>>>> > >>>>> Because later they do: > >>>>> > >>>>> vdsc_cfg->rc_buf_thresh[i] = rc_buf_thresh[i] >> 6; > >>>>> > >>>>>> > >>>>>> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L40 > >>>>>> > >>>>>> > >>>>>> Vs > >>>>>> > >>>>>> +static u16 dpu_dsc_rc_buf_thresh[DSC_NUM_BUF_RANGES - 1] = { > >>>>>> + 0x0e, 0x1c, 0x2a, 0x38, 0x46, 0x54, > >>>>>> + 0x62, 0x69, 0x70, 0x77, 0x79, 0x7b, 0x7d, 0x7e > >>>>>> +}; > >>>>> > >>>>> I'd prefer to have 896, 1792, etc. here, as those values come from the > >>>>> standard. As it's done in the Intel driver. > >>>>> > >>>> > >>>> Got it, thanks > >>>> > >>>>>> I dont know the AMD calculation very well to say that moving this > >>>>>> to the > >>>>>> helper is going to help. > >>>>> > >>>>> Those calculations correspond (more or less) at the first glance to > >>>>> what intel does for their newer generations. I think that's not our > >>>>> problem for now. > >>>>> > >>>> > >>>> Well, we have to figure out if each value matches and if each of > >>>> them come from the spec for us and i915 and from which section. So > >>>> it is unfortunately our problem. > >>> > >>> Otherwise it will have to be handled by Marijn, me or anybody else > >>> wanting to hack up the DSC code. Or by anybody adding DSC support to > >>> the next platform and having to figure out the difference between > >>> i915, msm and their platform. > >>> > >> > >> Yes, I wonder why the same doubt didn't arise when the other vendors > >> added their support both from other maintainers and others. > >> > >> Which makes me think that like I wrote in my previous response, these > >> are "recommended" values in the spec but its not mandatory. > > > > I think, it is because there were no other drivers to compare. In other > > words, for a first driver it is pretty logical to have everything > > handled on its own. As soon as we start getting other implementations of > > a feature, it becomes logical to think if the code can be generalized. > > This is what we see we with the HDCP series or with the code being moved > > to DP helpers. > > > > We were not the second, MSM was/is the third to add support for DSC afer > i915 and AMD. Thats what made me think why whoever was the second didnt > end up generalizing. Was it just missed out or was it intentionally left > in the vendor driver. I didn't count AMD here, since it calculates some of the params rather than using the fixed ones from the model. > > >> > >> Moving this to the drm_dsc_helper is generalizing the tables and not > >> giving room for the vendors to customize even if they want to (which > >> the spec does allow). > > > > That depends on the API you select. For example, in > > intel_dsc_compute_params() I see customization being applied to > > rc_buf_thresh in 6bpp case. I'd leave that to the i915 driver. > > > > Thanks for going through the i915 to figure out that the 6bpp is handled > in a customized way. So what you are saying is let the helper first fill > up the recommended values of the spec, whatever is changed from that let > the vendor driver override that. > > Thats where the case-by-case handling comes. > > Why not we do this way? Like you mentioned lets move these tables to the > drm_dsc_helper and let MSM driver first use those. > > Then in a separate patchset if i915 and AMD would like to move to that, > let them handle it for their respective drivers instead of MSM going > through whats customized for each calculation and doing it. > > I am hesitant to take up that effort. Writing a tool to convert model's rc_Nbpc_Mbpp_foo.cfg into C languages structures used by Intel code took 15-20 minutes. Plugging generated structures took another 5 minutes. I will send the patches later today or tomorrow, as I find a time slot to clean them. Thank you for spending more time on arguing than it took me to generate & verify the data. > > If the recommended values work for the vendor, they can clean it up and > move to the drm_dsc_helper themselves and preserving their > customizations rather than one vendor doing it for all of them. > > > In case the driver needs to perform customization of the params, nothing > > stops it drop applying after filling all the RC params in the > > drm_dsc_config struct via the generic helper. > > > > > >> So if this has any merit and if you or Marijn would like to take it > >> up, go for it. We would do the same thing as either of you would have > >> to in terms of figuring out the difference between msm and the i915 code. > >> > >> This is not a generic API we are trying to put in a helper, these are > >> hard-coded tables so there is a difference between looking at these Vs > >> looking at some common code which can move to the core. > >> > >>>> > >>>>>> > >>>>>> Also, i think its too risky to change other drivers to use > >>>>>> whatever math > >>>>>> we put in the drm_dsc_helper to compute thr RC params because > >>>>>> their code > >>>>>> might be computing and using this tables differently. > >>>>>> > >>>>>> Its too much ownership for MSM developers to move this to > >>>>>> drm_dsc_helper > >>>>>> and own that as it might cause breakage of basic DSC even if some > >>>>>> values > >>>>>> are repeated. > >>>>> > >>>>> It's time to stop thinking about ownership and start thinking about > >>>>> shared code. We already have two instances of DSC tables. I don't > >>>>> think having a third instance, which is a subset of an existing > >>>>> dataset, would be beneficial to anybody. > >>>>> AMD has complicated code which supports half-bit bpp and calculates > >>>>> some of the parameters. But sharing data with the i915 driver is > >>>>> straightforward. > >>>>> > >>>> > >>>> Sorry, but I would like to get an ack from i915 folks if this is going > >>>> to be useful to them if we move this to helper because we have to > >>>> look at every table. Not just one. > >>> > >>> Added i915 maintainers to the CC list for them to be able to answer. > >>> > >> > >> Thanks, lets wait to hear from them about where finally these tables > >> should go but thats can be taken up as a separate effort too. > >> > >>>> > >>>> Also, this is just 1.1, we will add more tables for 1.2. So we will > >>>> have to end up changing both 1.1 and 1.2 tables as they are > >>>> different for QC. > >>> > >>> I haven't heard back from Kuogee about the possible causes of using > >>> rc/qp values from 1.2 even for 1.1 panels. Maybe you can comment on > >>> that? In other words, can we always stick to the values from 1.2 > >>> standard? What will be the drawback? > >>> > >>> Otherwise, we'd have to have two different sets of values, like you > >>> do in your vendor driver. > >>> > >> > >> I have responded to this in the other email. > >> > >> All this being said, even if the rc tables move the drm_dsc_helper > >> either now or later on, we will still need MSM specific calculations > >> for many of the other encoder parameters (which are again either > >> hard-coded or calculated). Please refer to the > >> sde_dsc_populate_dsc_config() downstream. And yes, you will not find > >> those in the DP spec directly. > >> > >> So we will still need a dsc helper for MSM calculations to be common > >> for DSI / DP irrespective of where the tables go. > >> > >> So, lets finalize that first. > > > > I went on and trimmed sde_dsc_populate_dsc_config() to remove > > duplication with the drm_dsc_compute_rc_parameters() (which we already > > use for the MSM DSI DSC). > > > > Not much is left: > > > > dsc->first_line_bpg_offset set via the switch > > > > dsc->line_buf_depth = bpc + 1; > > dsc->mux_word_size = bpc > 10 ? DSC_MUX_WORD_SIZE_12_BPC: > > DSC_MUX_WORD_SIZE_8_10_BPC; > > > > if ((dsc->dsc_version_minor == 0x2) && (dsc->native_420)) > > dsc->nsl_bpg_offset = (2048 * > > (DIV_ROUND_UP(dsc->second_line_bpg_offset, > > (dsc->slice_height - 1)))); > > > > dsc->initial_scale_value = 8 * dsc->rc_model_size / > > (dsc->rc_model_size - dsc->initial_offset); > > > > > > mux_word_size comes from the standard (must) > > initial_scale_value calculation is recommended, but not required > > nsl_bpg_offset follows the standard (must), also see below (*). > > > > first_line_bpg_offset calculation differs between three drivers. The > > standard also provides a recommended formulas. I think we can leave it > > as is for now. > > > > I think, that mux_word_size and nsl_bpg_offset calculation should be > > moved to drm_dsc_compute_rc_parameters(), while leaving > > initial_scale_value in place (in the driver code). > > > > * I think nsl_bpg_offset is slightly incorrectly calculated. Standard > > demands that it is set to 'second_line_bpg_offset / (slice_height - 1), > > rounded up to 16 fraction bits', while SDE driver code sets it to the > > value rounded up to the next integer (having 16 fraction bits > > representation). > > > > In my opinion correct calculation should be: > > dsc->nsl_bpg_offset = DIV_ROUND_UP(2048 * dsc->second_line_bpg_offset, > > (dsc->slice_height - 1)); > > > > Could you please check, which one is correct according to the standard? > > > > > > Sure, i will check about nsl_bpg_offset. But sorry if I was not more > clear about this but sde_dsc_populate_dsc_config() is only one example > which from your analysis can be moved to the drm_dsc_helper() but not > the initial line calculation _dce_dsc_initial_line_calc(), > _dce_dsc_ich_reset_override_needed() , _dce_dsc_setup_helper(). The initial_line is already calculated in dpu_encoder.c. As for the _dce_dsc_ich_reset_override_needed(), I don't think we support partial updates in the upstream driver. > > All of these are again common between DSI and DP. > > So in addition to thinking about what can be moved to the drm_dsc_helper > also think about what is specific to MSM but common to DSI and DP modules. > > That was the bigger picture I was trying to convey. -- With best wishes Dmitry
