Date:   Mon, 27 Feb 2023 13:24:48 -0800
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        <quic_sbillaka@...cinc.com>, <linux-kernel@...r.kernel.org>,
        <vkoul@...nel.org>, <andersson@...nel.org>,
        <freedreno@...ts.freedesktop.org>, <dianders@...omium.org>,
        <dri-devel@...ts.freedesktop.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>, <agross@...nel.org>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        <marijn.suijten@...ainline.org>, <swboyd@...omium.org>,
        <sean@...rly.run>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions



On 2/27/2023 11:25 AM, Dmitry Baryshkov wrote:
> 27 февраля 2023 г. 19:59:35 GMT+02:00, Abhinav Kumar <quic_abhinavk@...cinc.com> пишет:
>>
>>
>> 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.
> 
> Getting rid of msm_display_dsc_config and then making use of drm_dsc_compute_rc_parameters() was bad enough. So, let's get things done in a good way now, rather than at some random point later.
> 

Alright, we will wait for your change then :)

> 
>>
>> 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.
> 
> But it is still the DPU thing. So, no problems.
> 

I am not fully convinced. We will wait for your post, then see how the 
code looks.

>>
>>>
>>>
> 

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