Message-ID: <c650e746-64c5-ce6b-933d-057349356b78@quicinc.com>
Date:   Mon, 27 Feb 2023 09:59:35 -0800
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        <dri-devel@...ts.freedesktop.org>, <robdclark@...il.com>,
        <sean@...rly.run>, <swboyd@...omium.org>, <dianders@...omium.org>,
        <vkoul@...nel.org>, <daniel@...ll.ch>, <airlied@...il.com>,
        <agross@...nel.org>, <andersson@...nel.org>,
        <quic_sbillaka@...cinc.com>, <marijn.suijten@...ainline.org>,
        <freedreno@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>
Subject: Re: [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions



On 2/27/2023 4:45 AM, Dmitry Baryshkov wrote:
> On Mon, 27 Feb 2023 at 01:49, Abhinav Kumar <quic_abhinavk@...cinc.com> 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@...cinc.com> 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@...cinc.com> 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.
> 

Great, we will wait for your patches. We didnt intend to spend time on 
this at this point. We always wanted to take it up in a separate series 
of moving the tables.

You preferred not to wait. Upto you.

So thanks for doing it.

>>
>> 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.
> 

_dce_dsc_initial_line_calc which will get expanded with v1.2 gets added 
has much more than whats there in upstream today.

Dumping everything in dpu_encoder is not the solution. Sorry.

> 
> 

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