LKML Archive on
help / color / mirror / Atom feed
From: Benjamin Gaignard <>
To: Ezequiel Garcia <>,
	John Cox <>
Cc: Nicolas Dufresne <>,
	Mauro Carvalho Chehab <>,
	Hans Verkuil <>,
	linux-media <>,
	Linux Kernel Mailing List <>,
	Collabora Kernel ML <>
Subject: Re: [PATCH] media: hevc: fix pictures lists type
Date: Fri, 27 Aug 2021 17:26:13 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Le 27/08/2021 à 14:40, Ezequiel Garcia a écrit :
> On Fri, 27 Aug 2021 at 09:36, John Cox <> wrote:
>>> Le 27/08/2021 à 12:10, John Cox a écrit :
>>>>> Le 26/08/2021 à 18:09, Nicolas Dufresne a écrit :
>>>>>> Le lundi 23 août 2021 à 12:35 +0100, John Cox a écrit :
>>>>>>> Hi
>>>>>>>> Le 23/08/2021 à 11:50, John Cox a écrit :
>>>>>>>>>> The lists embedded Picture Order Count values which are s32 so their type
>>>>>>>>>> most be s32 and not u8.
>>>>>>>>> I'm not convinced that you can't calculate all of those lists from the
>>>>>>>>> info already contained in the DPB array so this is probably redundant
>>>>>>>>> info though I grant that having the list pre-calced might make your life
>>>>>>>>> easier, and the userland side will have calculated the lists to
>>>>>>>>> calculate other required things so it isn't much extra work for it.
>>>>>>>> Yes the userland have already compute these lists and the number of items
>>>>>>>> in each of them.
>>>>>>>> Build them in the kernel would means to also compute the values of NumPocStCurrBefore,
>>>>>>>> NumPocStCurrAfter, NumPocLtCurr, NumPocStCurrAfter, NumPocStCurrBefore and NumPocLtCurr
>>>>>>>> and that requires information (NumNegativePics, NumPositivePics...) not provided to the kernel.
>>>>>>>> Since it have to be done in userland anyway, I'm reluctant to modify the API to redo in the kernel.
>>>>>>> Well, fair enough, I'm not going to argue
>>>>>>>>> Even if you do need the lists wouldn't it be a better idea to have them
>>>>>>>>> as indices into the DPB (you can't have a frame in any of those lists
>>>>>>>>> that isn't in the DPB) which already contains POCs then it will still
>>>>>>>>> fit into u8 and be smaller?
>>>>>>>> Hantro HW works with indexes but I think it is more simple to send PoC rather than indexes.
>>>>>>> I'd disagree but as I don't use the info I'm not concerned. Though I
>>>>>>> think I should point out that when Hantro converts the POCs to indicies
>>>>>>> it compares the now s32 POC in these lists with the u16 POC in the DPB
>>>>>>> so you might need to fix that too; by std (8.3.1) no POC diff can be
>>>>>>> outside s16 so you can mask & compare or use u16 POCs in the lists or
>>>>>>> s32 in the DPB.
>>>>>> Fun fact, my interpretation with the API when I drafted GStreamer support was
>>>>>> that it was DPB indexes:
>>>>>> It felt quite natural to be, since this is also how we pass references for l0/l1
>>>>>> (unused by hantro I guess).
>>>>>> Looking at old rkvdec code as a refresher:
>>>>>>      for (j = 0; j < run->num_slices; j++) {
>>>>>>                    sl_params = &run->slices_params[j];
>>>>>>                    dpb = sl_params->dpb;
>>>>>>                    hw_ps = &priv_tbl->rps[j];
>>>>>>                    memset(hw_ps, 0, sizeof(*hw_ps));
>>>>>>                    for (i = 0; i <= sl_params->num_ref_idx_l0_active_minus1; i++) {
>>>>>>                            WRITE_RPS(!!(dpb[sl_params->ref_idx_l0[i]].rps == V4L2_HEVC_DPB_ENTRY_RPS_LT_CURR),
>>>>>>                                      REF_PIC_LONG_TERM_L0(i));
>>>>>>                            WRITE_RPS(sl_params->ref_idx_l0[i], REF_PIC_IDX_L0(i));
>>>>>>                    }
>>>>>>                    for (i = 0; i <= sl_params->num_ref_idx_l1_active_minus1; i++) {
>>>>>>                            WRITE_RPS(!!(dpb[sl_params->ref_idx_l1[i]].rps == V4L2_HEVC_DPB_ENTRY_RPS_LT_CURR),
>>>>>>                                      REF_PIC_LONG_TERM_L1(i));
>>>>>>                            WRITE_RPS(sl_params->ref_idx_l1[i], REF_PIC_IDX_L1(i));
>>>>>>                    }
>>>>>> This is code is clearly unsafe, but now I remember that dpb_entry has a flag
>>>>>> "rps". So we know from the DPB in which of the list the reference lives, if any.
>>>>>> In the case of RKVDEC the HW only cares to know if this is long term or not.
>>>>>> So without looking at the spec, is that dpb represention enough to reconstruct
>>>>>> these array ? If we pass these array, shall we keep the rps flag ? I think a
>>>>>> little step back and cleanup will be needed. I doubt there is a single answer,
>>>>>> perhaps list what others do (VA, DXVA, NVDEC, Khronos, etc) and we can
>>>>>> collectively decide were we want V4L2 to sit ?
>>>>> I have done some tests with Hantro driver and look at the spec, the order of the PoC
>>>>> in the reference lists matters. You can deducted the order for DPB rps flags.
>>>>> I would suggest to remove rps flags to avoid information duplication.
>>>> I want the DPB rps member for long term reference marking.  I don't care
>>>> about before / after, but LTR can't be deduced from PoC and if you are
>>>> going to keep the member you might as well keep before / after.
>>> Ok so keep like it is.
>>> In this case my patch is enough, right ?
> The problem with the patch is that it breaks existing userspace.
> Currently, there's no upstreamed userspace so this is not a huge
> deal.
> However, it's definitely not a good practice. Even if these are
> staging controls, I think a proper action item is to start discussing
> what's missing on the HEVC interface as a whole, so it can be
> moved to stable.

I do agree I think it could the time to talk about moving the API to stable.
My plan is to get this patch merge before sending a RFC to move the API.


> Otherwise, it almost feels like bikeshading.
> Thanks,
> Ezequiel

  reply	other threads:[~2021-08-27 15:26 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-23  8:29 Benjamin Gaignard
2021-08-23  9:50 ` John Cox
2021-08-23 11:17   ` Benjamin Gaignard
2021-08-23 11:35     ` John Cox
2021-08-26 16:09       ` Nicolas Dufresne
2021-08-27  8:55         ` Benjamin Gaignard
2021-08-27 10:10           ` John Cox
2021-08-27 11:35             ` Benjamin Gaignard
2021-08-27 12:36               ` John Cox
2021-08-27 12:40                 ` Ezequiel Garcia
2021-08-27 15:26                   ` Benjamin Gaignard [this message]
2021-08-27 18:46                     ` Ezequiel Garcia

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \
    --subject='Re: [PATCH] media: hevc: fix pictures lists type' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).