Hi, Le samedi 18 mai 2019 à 12:04 +0200, Jernej Škrabec a écrit : > Dne sobota, 18. maj 2019 ob 11:50:37 CEST je Paul Kocialkowski napisal(a): > > Hi, > > > > On Fri, 2019-05-17 at 16:43 -0400, Nicolas Dufresne wrote: > > > Le jeudi 16 mai 2019 à 20:45 +0200, Paul Kocialkowski a écrit : > > > > Hi, > > > > > > > > Le jeudi 16 mai 2019 à 14:24 -0400, Nicolas Dufresne a écrit : > > > > > Le mercredi 15 mai 2019 à 22:59 +0200, Paul Kocialkowski a écrit : > > > > > > Hi, > > > > > > > > > > > > Le mercredi 15 mai 2019 à 14:54 -0400, Nicolas Dufresne a écrit : > > > > > > > Le mercredi 15 mai 2019 à 19:42 +0200, Paul Kocialkowski a écrit : > > > > > > > > Hi, > > > > > > > > > > > > > > > > Le mercredi 15 mai 2019 à 10:42 -0400, Nicolas Dufresne a écrit > : > > > > > > > > > Le mercredi 15 mai 2019 à 12:09 +0200, Paul Kocialkowski a > écrit : > > > > > > > > > > Hi, > > > > > > > > > > > > > > > > > > > > With the Rockchip stateless VPU driver in the works, we now > > > > > > > > > > have a > > > > > > > > > > better idea of what the situation is like on platforms other > > > > > > > > > > than > > > > > > > > > > Allwinner. This email shares my conclusions about the > > > > > > > > > > situation and how > > > > > > > > > > we should update the MPEG-2, H.264 and H.265 controls > > > > > > > > > > accordingly. > > > > > > > > > > > > > > > > > > > > - Per-slice decoding > > > > > > > > > > > > > > > > > > > > We've discussed this one already[0] and Hans has submitted a > > > > > > > > > > patch[1] > > > > > > > > > > to implement the required core bits. When we agree it looks > > > > > > > > > > good, we > > > > > > > > > > should lift the restriction that all slices must be > > > > > > > > > > concatenated and > > > > > > > > > > have them submitted as individual requests. > > > > > > > > > > > > > > > > > > > > One question is what to do about other controls. I feel like > > > > > > > > > > it would > > > > > > > > > > make sense to always pass all the required controls for > > > > > > > > > > decoding the > > > > > > > > > > slice, including the ones that don't change across slices. > > > > > > > > > > But there > > > > > > > > > > may be no particular advantage to this and only downsides. > > > > > > > > > > Not doing it > > > > > > > > > > and relying on the "control cache" can work, but we need to > > > > > > > > > > specify > > > > > > > > > > that only a single stream can be decoded per opened instance > > > > > > > > > > of the > > > > > > > > > > v4l2 device. This is the assumption we're going with for > > > > > > > > > > handling > > > > > > > > > > multi-slice anyway, so it shouldn't be an issue. > > > > > > > > > > > > > > > > > > My opinion on this is that the m2m instance is a state, and > > > > > > > > > the driver > > > > > > > > > should be responsible of doing time-division multiplexing > > > > > > > > > across > > > > > > > > > multiple m2m instance jobs. Doing the time-division > > > > > > > > > multiplexing in > > > > > > > > > userspace would require some sort of daemon to work properly > > > > > > > > > across > > > > > > > > > processes. I also think the kernel is better place for doing > > > > > > > > > resource > > > > > > > > > access scheduling in general. > > > > > > > > > > > > > > > > I agree with that yes. We always have a single m2m context and > > > > > > > > specific > > > > > > > > controls per opened device so keeping cached values works out > > > > > > > > well. > > > > > > > > > > > > > > > > So maybe we shall explicitly require that the request with the > > > > > > > > first > > > > > > > > slice for a frame also contains the per-frame controls. > > > > > > > > > > > > > > > > > > - Annex-B formats > > > > > > > > > > > > > > > > > > > > I don't think we have really reached a conclusion on the > > > > > > > > > > pixel formats > > > > > > > > > > we want to expose. The main issue is how to deal with codecs > > > > > > > > > > that need > > > > > > > > > > the full slice NALU with start code, where the slice_header > > > > > > > > > > is > > > > > > > > > > duplicated in raw bitstream, when others are fine with just > > > > > > > > > > the encoded > > > > > > > > > > slice data and the parsed slice header control. > > > > > > > > > > > > > > > > > > > > My initial thinking was that we'd need 3 formats: > > > > > > > > > > - One that only takes only the slice compressed data > > > > > > > > > > (without raw slice > > > > > > > > > > header and start code); > > > > > > > > > > - One that takes both the NALU data (including start code, > > > > > > > > > > raw header > > > > > > > > > > and compressed data) and slice header controls; > > > > > > > > > > - One that takes the NALU data but no slice header. > > > > > > > > > > > > > > > > > > > > But I no longer think the latter really makes sense in the > > > > > > > > > > context of > > > > > > > > > > stateless video decoding. > > > > > > > > > > > > > > > > > > > > A side-note: I think we should definitely have data offsets > > > > > > > > > > in every > > > > > > > > > > case, so that implementations can just push the whole NALU > > > > > > > > > > regardless > > > > > > > > > > of the format if they're lazy. > > > > > > > > > > > > > > > > > > I realize that I didn't share our latest research on the > > > > > > > > > subject. So a > > > > > > > > > slice in the original bitstream is formed of the following > > > > > > > > > blocks > > > > > > > > > > > > > > > > > > (simplified): > > > > > > > > > [nal_header][nal_type][slice_header][slice] > > > > > > > > > > > > > > > > Thanks for the details! > > > > > > > > > > > > > > > > > nal_header: > > > > > > > > > This one is a header used to locate the start and the end of > > > > > > > > > the of a > > > > > > > > > NAL. There is two standard forms, the ANNEX B / start code, a > > > > > > > > > sequence > > > > > > > > > of 3 bytes 0x00 0x00 0x01, you'll often see 4 bytes, the first > > > > > > > > > byte > > > > > > > > > would be a leading 0 from the previous NAL padding, but this > > > > > > > > > is also > > > > > > > > > totally valid start code. The second form is the AVC form, > > > > > > > > > notably used > > > > > > > > > in ISOMP4 container. It simply is the size of the NAL. You > > > > > > > > > must keep > > > > > > > > > your buffer aligned to NALs in this case as you cannot scan > > > > > > > > > from random > > > > > > > > > location. > > > > > > > > > > > > > > > > > > nal_type: > > > > > > > > > It's a bit more then just the type, but it contains at least > > > > > > > > > the > > > > > > > > > information of the nal type. This has different size on H.264 > > > > > > > > > and HEVC > > > > > > > > > but I know it's size is in bytes. > > > > > > > > > > > > > > > > > > slice_header: > > > > > > > > > This contains per slice parameters, like the modification > > > > > > > > > lists to > > > > > > > > > apply on the references. This one has a size in bits, not in > > > > > > > > > bytes. > > > > > > > > > > > > > > > > > > slice: > > > > > > > > > I don't really know what is in it exactly, but this is the > > > > > > > > > data used to > > > > > > > > > decode. This bit has a special coding called the > > > > > > > > > anti-emulation, which > > > > > > > > > prevents a start-code from appearing in it. This coding is > > > > > > > > > present in > > > > > > > > > both forms, ANNEX-B or AVC (in GStreamer and some reference > > > > > > > > > manual they > > > > > > > > > call ANNEX-B the bytestream format). > > > > > > > > > > > > > > > > > > So, what we notice is that what is currently passed through > > > > > > > > > Cedrus > > > > > > > > > > > > > > > > > > driver: > > > > > > > > > [nal_type][slice_header][slice] > > > > > > > > > > > > > > > > > > This matches what is being passed through VA-API. We can > > > > > > > > > understand > > > > > > > > > that stripping off the slice_header would be hard, since it's > > > > > > > > > size is > > > > > > > > > in bits. Instead we pass size and header_bit_size in > > > > > > > > > slice_params. > > > > > > > > > > > > > > > > True, there is that. > > > > > > > > > > > > > > > > > About Rockchip. RK3288 is a Hantro G1 and has a bit called > > > > > > > > > start_code_e, when you turn this off, you don't need start > > > > > > > > > code. As a > > > > > > > > > side effect, the bitstream becomes identical. We do now know > > > > > > > > > that it > > > > > > > > > works with the ffmpeg branch implement for cedrus. > > > > > > > > > > > > > > > > Oh great, that makes life easier in the short term, but I guess > > > > > > > > the > > > > > > > > issue could arise on another decoder sooner or later. > > > > > > > > > > > > > > > > > Now what's special about Hantro G1 (also found on IMX8M) is > > > > > > > > > that it > > > > > > > > > take care for us of reading and executing the modification > > > > > > > > > lists found > > > > > > > > > in the slice header. Mostly because I very disliked having to > > > > > > > > > pass the > > > > > > > > > p/b0/b1 parameters, is that Boris implemented in the driver > > > > > > > > > the > > > > > > > > > transformation from the DPB entries into this p/b0/b1 list. > > > > > > > > > These list > > > > > > > > > a standard, it's basically implementing 8.2.4.1 and 8.2.4.2. > > > > > > > > > the > > > > > > > > > following section is the execution of the modification list. > > > > > > > > > As this > > > > > > > > > list is not modified, it only need to be calculated per frame. > > > > > > > > > As a > > > > > > > > > result, we don't need these new lists, and we can work with > > > > > > > > > the same > > > > > > > > > H264_SLICE format as Cedrus is using. > > > > > > > > > > > > > > > > Yes but I definitely think it makes more sense to pass the list > > > > > > > > modifications rather than reconstructing those in the driver > > > > > > > > from a > > > > > > > > full list. IMO controls should stick to the bitstream as close > > > > > > > > as > > > > > > > > possible. > > > > > > > > > > > > > > For Hantro and RKVDEC, the list of modification is parsed by the > > > > > > > IP > > > > > > > from the slice header bits. Just to make sure, because I myself > > > > > > > was > > > > > > > confused on this before, the slice header does not contain a list > > > > > > > of > > > > > > > references, instead it contains a list modification to be applied > > > > > > > to > > > > > > > the reference list. I need to check again, but to execute these > > > > > > > modification, you need to filter and sort the references in a > > > > > > > specific > > > > > > > order. This should be what is defined in the spec as 8.2.4.1 and > > > > > > > 8.2.4.2. Then 8.2.4.3 is the process that creates the l0/l1. > > > > > > > > > > > > > > The list of references is deduced from the DPB. The DPB, which I > > > > > > > thinks > > > > > > > should be rename as "references", seems more useful then p/b0/b1, > > > > > > > since > > > > > > > this is the data that gives use the ability to implementing glue > > > > > > > in the > > > > > > > driver to compensate some HW differences. > > > > > > > > > > > > > > In the case of Hantro / RKVDEC, we think it's natural to build the > > > > > > > HW > > > > > > > specific lists (p/b0/b1) from the references rather then adding HW > > > > > > > specific list in the decode_params structure. The fact these lists > > > > > > > are > > > > > > > standard intermediate step of the standard is not that important. > > > > > > > > > > > > Sorry I got confused (once more) about it. Boris just explained the > > > > > > same thing to me over IRC :) Anyway my point is that we want to pass > > > > > > what's in ffmpeg's short and long term ref lists, and name them that > > > > > > instead of dpb. > > > > > > > > > > > > > > > Now, this is just a start. For RK3399, we have a different > > > > > > > > > CODEC > > > > > > > > > design. This one does not have the start_code_e bit. What the > > > > > > > > > IP does, > > > > > > > > > is that you give it one or more slice per buffer, setup the > > > > > > > > > params, > > > > > > > > > start decoding, but the decoder then return the location of > > > > > > > > > the > > > > > > > > > following NAL. So basically you could offload the scanning of > > > > > > > > > start > > > > > > > > > code to the HW. That being said, with the driver layer in > > > > > > > > > between, that > > > > > > > > > would be amazingly inconvenient to use, and with Boyer-more > > > > > > > > > algorithm, > > > > > > > > > it is pretty cheap to scan this type of start-code on CPU. But > > > > > > > > > the > > > > > > > > > feature that this allows is to operate in frame mode. In this > > > > > > > > > mode, you > > > > > > > > > have 1 interrupt per frame. > > > > > > > > > > > > > > > > I'm not sure there is any interest in exposing that from > > > > > > > > userspace and > > > > > > > > my current feeling is that we should just ditch support for > > > > > > > > per-frame > > > > > > > > decoding altogether. I think it mixes decoding with notions that > > > > > > > > are > > > > > > > > higher-level than decoding, but I agree it's a blurry line. > > > > > > > > > > > > > > I'm not worried about this either. We can already support that by > > > > > > > copying the bitstream internally to the driver, though zero-copy > > > > > > > with > > > > > > > this would require a new format, the one we talked about, > > > > > > > SLICE_ANNEX_B. > > > > > > > > > > > > Right, but what I'm thinking about is making that the one and only > > > > > > format. The rationale is that it's always easier to just append a > > > > > > start > > > > > > code from userspace if needed. And we need a bit offset to the slice > > > > > > data part anyway, so it doesn't hurt to require a few extra bits to > > > > > > have the whole thing that will work in every situation. > > > > > > > > > > What I'd like is to eventually allow zero-copy (aka userptr) into the > > > > > driver. If you make the start code mandatory, any decoding from ISOMP4 > > > > > (.mp4, .mov) will require a full bitstream copy in userspace to add > > > > > the > > > > > start code (unless you hack your allocation in your demuxer, but it's > > > > > a > > > > > bit complicated since this code might come from two libraries). In > > > > > ISOMP4, you have an AVC header, which is just the size of the NAL that > > > > > follows. > > > > > > > > Well, I think we have to do a copy from system memory to the buffer > > > > allocated by v4l2 anyway. Our hardware pipelines can reasonably be > > > > expected not to have any MMU unit and not allow sg import anyway. > > > > > > The Rockchip has an mmu. You need one copy at least indeed, > > > > Is the MMU in use currently? That can make things troublesome if we run > > into a case where the VPU has MMU and deals with scatter-gather while > > the display part doesn't. As far as I know, there's no way for > > userspace to know whether a dma-buf-exported buffer is backed by CMA or > > by scatter-gather memory. This feels like a major issue for using dma- > > buf, since userspace can't predict whether a buffer exported on one > > device can be imported on another when building its pipeline. > > FYI, Allwinner H6 also has IOMMU, it's just that there is no mainline driver > for it yet. It is supported for display, both VPUs and some other devices. I > think no sane SoC designer would left out one or another unit without IOMMU > support, that just calls for troubles, as you pointed out. Right right, I've been following that from a distance :) Indeed I think it's realistic to expect that for now, but it may not play out so well in the long term. For instance, maybe connecting a USB display would require CMA when the rest of the system can do with sg. I think it would really be useful for userspace to have a way to test whether a buffer can be imported from one device to another. It feels better than indicating where the memory lives, since there are countless cases where additional restrictions apply too. Cheers, Paul > Best regards, > Jernej > > > > e.g. file > > > to mem, or udpsocket to mem. But right now, let's say with ffmpeg/mpeg- > > > ts, first you need to copy the MPEG TS to mem, then to demux you copy > > > that H264 stream to another buffer, you then copy in the parser, > > > removing the start-code and finally copy in the accelerator, adding the > > > start code. If the driver would allow userptr, it would be unusable. > > > > > > GStreamer on the other side implement lazy conversion, so it would copy > > > the mpegts to mem, copy to demux, aggregate (with lazy merging) in the > > > parser (but stream format is negotiation, so it keeps the start-code). > > > If you request alignment=au, you have full frame of buffers, so if your > > > driver could do userptr, you can same that extra copy. > > > > > > Now, if we demux an MP4 it's the same, the parser will need do a full > > > copy instead of lazy aggregation in order to prepend the start code > > > (since it had an AVC header). But userptr could save a copy. > > > > > > If the driver requires no nal prefix, then we could just pass a > > > slightly forward point to userptr and avoid ACV to ANNEX-B conversion, > > > which is a bit slower (even know it's nothing compare to the full > > > copies we already do. > > > > > > That was my argument in favour for no NAL prefix in term of efficiency, > > > and it does not prevent adding a control to enable start-code for cases > > > it make sense. > > > > I see, so the internal arcitecture of userspace software may not be a > > good fit for adding these bits and it could hurt performance a bit. > > That feels like a significant downside. > > > > > > So with that in mind, asking userspace to add a startcode it already > > > > knows doesn't seem to be asking too much. > > > > > > > > > On the other end, the data_offset thing is likely just a thing for the > > > > > RK3399 to handle, it does not affect RK3288, Cedrus or IMX8M. > > > > > > > > Well, I think it's best to be fool-proof here and just require that > > > > start code. We should also have per-slice bit offsets to the different > > > > parts anyway, so drivers that don't need it can just ignore it. > > > > > > > > In extreme cases where there is some interest in doing direct buffer > > > > import without doing a copy in userspace, userspace could trick the > > > > format and avoid a copy by not providing the start-code (assuming it > > > > knows it doesn't need it) and specifying the bit offsets accordingly. > > > > That'd be a hack for better performance, and it feels better to do > > > > things in this order rather than having to hack around in the drivers > > > > that need the start code in every other case. > > > > > > So basically, you and Tomas are both strongly in favour of adding > > > ANNEX-B start-code to the current uAPI. I have digged into Cedrus > > > registers, and it seems that it does have start-code scanning support. > > > I'm not sure it can do "full-frame" decoding, 1 interrupt per frame > > > like the RK do. That requires the IP to deal with the modifications > > > lists, which are per slices. > > > > Actually the bitstream parser won't reconfigure the pipeline > > configuration registers, it's only around for userspace to avoid > > implementing bitstream parsing, but it's a standalone thing. > > > > So if we want to do full-frame decoding we always need to reconfigure > > our pipeline (or do it like we do currently and just use one of the > > per-slice configuration and hope for the best). > > > > Do we have more information on the RK3399 and what it requires exactly? > > (Just to make sure it's not another issue altogether.) > > > > > My question is, are you willing to adapt the Cedrus driver to support > > > receiving start-code ? And will this have a performance impact or not ? > > > On RK side, it's really just about flipping 1 bit. > > > > > > On the Rockchip side, Tomas had concern about CPU wakeup and the fact > > > that we didn't aim at supporting passing multiple slices at once to the > > > IP (something RK supports). It's important to understand that multi- > > > slice streams are relatively rare and mostly used for low-latency / > > > video conferencing. So aggregating in these case defeats the purpose of > > > using slices. So I think RK feature is not very important. > > > > Agreed, let's aim for low-latency as a standard. > > > > > Of course, I do believe that long term we will want to expose bot > > > stream formats on RK (because the HW can do that), so then userspace > > > can just pick the best when available. So that boils down to our first > > > idea, shall we expose _SLICE_A and _SLICE_B or something like this ? > > > Now that we have progressed on the matter, I'm quite in favour of > > > having _SLICE in the first place, with the preferred format that > > > everyone should support, and allow for variants later. Now, if we make > > > one mandatory, we could also just have a menu control to allow other > > > formats. > > > > That seems fairly reasonable to me, and indeed, having one preferred > > format at first seems to be a good move. > > > > > > > > To me the breaking point was about having the slice header both in > > > > > > raw > > > > > > bitstream and parsed forms. Since we agree that's fine, we might as > > > > > > well push it to its logical conclusion and include all the bits that > > > > > > can be useful. > > > > > > > > > > To take your words, the bits that contain useful information starts > > > > > from the NAL type byte, exactly were the data was cut by VA-API and > > > > > the > > > > > current uAPI. > > > > > > > > Agreed, but I think that the advantages of always requiring the start > > > > code outweigh the potential (yet quite unlikely) downsides. > > > > > > > > > > > > > But it also support slice mode, with an > > > > > > > > > interrupt per slice, which is what we decided to use. > > > > > > > > > > > > > > > > Easier for everyone and probably better for latency as well :) > > > > > > > > > > > > > > > > > So in this case, indeed we strictly require on start-code. > > > > > > > > > Though, to > > > > > > > > > me this is not a great reason to make a new fourcc, so we will > > > > > > > > > try and > > > > > > > > > use (data_offset = 3) in order to make some space for that > > > > > > > > > start code, > > > > > > > > > and write it down in the driver. This is to be continued, we > > > > > > > > > will > > > > > > > > > report back on this later. This could have some side effect in > > > > > > > > > the > > > > > > > > > ability to import buffers. But most userspace don't try to do > > > > > > > > > zero-copy > > > > > > > > > on the encoded size and just copy anyway. > > > > > > > > > > > > > > > > > > To my opinion, having a single format is a big deal, since > > > > > > > > > userspace > > > > > > > > > will generally be developed for one specific HW and we would > > > > > > > > > endup with > > > > > > > > > fragmented support. What we really want to achieve is having a > > > > > > > > > driver > > > > > > > > > interface which works across multiple HW, and I think this is > > > > > > > > > quite > > > > > > > > > possible. > > > > > > > > > > > > > > > > I agree with that. The more I think about it, the more I believe > > > > > > > > we > > > > > > > > should just pass the whole > > > > > > > > [nal_header][nal_type][slice_header][slice] > > > > > > > > and the parsed list in every scenario. > > > > > > > > > > > > > > What I like of the cut at nal_type, is that there is only format. > > > > > > > If we > > > > > > > cut at nal_header, then we need to expose 2 formats. And it makes > > > > > > > our > > > > > > > API similar to other accelerator API, so it's easy to "convert" > > > > > > > existing userspace. > > > > > > > > > > > > Unless we make that cut the single one and only true cut that shall > > > > > > supersed all other cuts :) > > > > > > > > > > That's basically what I've been trying to do, kill this _RAW/ANNEX_B > > > > > thing and go back to our first idea. > > > > > > > > Right, in the end I think we should go with: > > > > V4L2_PIX_FMT_MPEG2_SLICE > > > > V4L2_PIX_FMT_H264_SLICE > > > > V4L2_PIX_FMT_HEVC_SLICE > > > > > > > > And just require raw bitstream for the slice with emulation-prevention > > > > bits included. > > > > > > That's should be the set of format we start with indeed. The single > > > format for which software gets written and tested, making sure software > > > support is not fragmented, and other variants should be something to > > > opt-in. > > > > Cheers for that! > > > > Paul > > > > > > Cheers, > > > > > > > > Paul > > > > > > > > > > > > For H.265, our decoder needs some information from the NAL type > > > > > > > > too. > > > > > > > > We currently extract that in userspace and stick it to the > > > > > > > > slice_header, but maybe it would make more sense to have drivers > > > > > > > > parse > > > > > > > > that info from the buffer if they need it. On the other hand, it > > > > > > > > seems > > > > > > > > quite common to pass information from the NAL type, so maybe we > > > > > > > > should > > > > > > > > either make a new control for it or have all the fields in the > > > > > > > > slice_header (which would still be wrong in terms of matching > > > > > > > > bitstream > > > > > > > > description). > > > > > > > > > > > > > > Even in userspace, it's common to just parse this in place, it's a > > > > > > > simple mask. But yes, if we don't have it yet, we should expose > > > > > > > the NAL > > > > > > > type, it would be cleaner. > > > > > > > > > > > > Right, works for me. > > > > > > > > > > Ack. > > > > > > > > > > > Cheers, > > > > > > > > > > > > Paul > > > > > > > > > > > > > > > > - Dropping the DPB concept in H.264/H.265 > > > > > > > > > > > > > > > > > > > > As far as I could understand, the decoded picture buffer > > > > > > > > > > (DPB) is a > > > > > > > > > > concept that only makes sense relative to a decoder > > > > > > > > > > implementation. The > > > > > > > > > > spec mentions how to manage it with the Hypothetical > > > > > > > > > > reference decoder > > > > > > > > > > (Annex C), but that's about it. > > > > > > > > > > > > > > > > > > > > What's really in the bitstream is the list of modified > > > > > > > > > > short-term and > > > > > > > > > > long-term references, which is enough for every decoder. > > > > > > > > > > > > > > > > > > > > For this reason, I strongly believe we should stop talking > > > > > > > > > > about DPB in > > > > > > > > > > the controls and just pass these lists agremented with > > > > > > > > > > relevant > > > > > > > > > > information for userspace. > > > > > > > > > > > > > > > > > > > > I think it should be up to the driver to maintain a DPB and > > > > > > > > > > we could > > > > > > > > > > have helpers for common cases. For instance, the rockchip > > > > > > > > > > decoder needs > > > > > > > > > > to keep unused entries around[2] and cedrus has the same > > > > > > > > > > requirement > > > > > > > > > > for H.264. However for cedrus/H.265, we don't need to do any > > > > > > > > > > book- > > > > > > > > > > keeping in particular and can manage with the lists from the > > > > > > > > > > bitstream > > > > > > > > > > directly. > > > > > > > > > > > > > > > > > > As discusses today, we still need to pass that list. It's > > > > > > > > > being index > > > > > > > > > by the HW to retrieve the extra information we have collected > > > > > > > > > about the > > > > > > > > > status of the reference frames. In the case of Hantro, which > > > > > > > > > process > > > > > > > > > the modification list from the slice header for us, we also > > > > > > > > > need that > > > > > > > > > list to construct the unmodified list. > > > > > > > > > > > > > > > > > > So the problem here is just a naming problem. That list is not > > > > > > > > > really a > > > > > > > > > DPB. It is just the list of long-term/short-term references > > > > > > > > > with the > > > > > > > > > status of these references. So maybe we could just rename as > > > > > > > > > references/reference_entry ? > > > > > > > > > > > > > > > > What I'd like to pass is the diff to the references list, as > > > > > > > > ffmpeg > > > > > > > > currently provides for v4l2 request and vaapi (probably vdpau > > > > > > > > too). No > > > > > > > > functional change here, only that we should stop calling it a > > > > > > > > DPB, > > > > > > > > which confuses everyone. > > > > > > > > > > > > > > Yes. > > > > > > > > > > > > > > > > > - Using flags > > > > > > > > > > > > > > > > > > > > The current MPEG-2 controls have lots of u8 values that can > > > > > > > > > > be > > > > > > > > > > represented as flags. Using flags also helps with padding. > > > > > > > > > > It's unlikely that we'll get more than 64 flags, so using a > > > > > > > > > > u64 by > > > > > > > > > > default for that sounds fine (we definitely do want to keep > > > > > > > > > > some room > > > > > > > > > > available and I don't think using 32 bits as a default is > > > > > > > > > > good enough). > > > > > > > > > > > > > > > > > > > > I think H.264/HEVC per-control flags should also be moved to > > > > > > > > > > u64. > > > > > > > > > > > > > > > > > > Make sense, I guess bits (member : 1) are not allowed in uAPI > > > > > > > > > right ? > > > > > > > > > > > > > > > > Mhh, even if they are, it makes it much harder to verify 32/64 > > > > > > > > bit > > > > > > > > alignment constraints (we're dealing with 64-bit platforms that > > > > > > > > need to > > > > > > > > have 32-bit userspace and compat_ioctl). > > > > > > > > > > > > > > I see, thanks. > > > > > > > > > > > > > > > > > - Clear split of controls and terminology > > > > > > > > > > > > > > > > > > > > Some codecs have explicit NAL units that are good fits to > > > > > > > > > > match as > > > > > > > > > > controls: e.g. slice header, pps, sps. I think we should > > > > > > > > > > stick to the > > > > > > > > > > bitstream element names for those. > > > > > > > > > > > > > > > > > > > > For H.264, that would suggest the following changes: > > > > > > > > > > - renaming v4l2_ctrl_h264_decode_param to > > > > > > > > > > v4l2_ctrl_h264_slice_header; > > > > > > > > > > > > > > > > > > Oops, I think you meant slice_prams ? decode_params matches > > > > > > > > > the > > > > > > > > > information found in SPS/PPS (combined?), while slice_params > > > > > > > > > matches > > > > > > > > > the information extracted (and executed in case of l0/l1) from > > > > > > > > > the > > > > > > > > > slice headers. > > > > > > > > > > > > > > > > Yes you're right, I mixed them up. > > > > > > > > > > > > > > > > > That being said, to me this name wasn't confusing, since > > > > > > > > > > > > > > > > > > it's not just the slice header, and it's per slice. > > > > > > > > > > > > > > > > Mhh, what exactly remains in there and where does it originate > > > > > > > > in the > > > > > > > > bitstream? Maybe it wouldn't be too bad to have one control per > > > > > > > > actual > > > > > > > > group of bitstream elements. > > > > > > > > > > > > > > > > > > - killing v4l2_ctrl_h264_decode_param and having the > > > > > > > > > > reference lists > > > > > > > > > > where they belong, which seems to be slice_header; > > > > > > > > > > > > > > > > > > There reference list is only updated by userspace (through > > > > > > > > > it's DPB) > > > > > > > > > base on the result of the last decoding step. I was very > > > > > > > > > confused for a > > > > > > > > > moment until I realize that the lists in the slice_header are > > > > > > > > > just a > > > > > > > > > list of modification to apply to the reference list in order > > > > > > > > > to produce > > > > > > > > > l0 and l1. > > > > > > > > > > > > > > > > Indeed, and I'm suggesting that we pass the modifications only, > > > > > > > > which > > > > > > > > would fit a slice_header control. > > > > > > > > > > > > > > I think I made my point why we want the dpb -> references. I'm > > > > > > > going to > > > > > > > validate with the VA driver now, to see if the references list > > > > > > > there is > > > > > > > usable with our code. > > > > > > > > > > > > > > > Cheers, > > > > > > > > > > > > > > > > Paul > > > > > > > > > > > > > > > > > > I'm up for preparing and submitting these control changes > > > > > > > > > > and updating > > > > > > > > > > cedrus if they seem agreeable. > > > > > > > > > > > > > > > > > > > > What do you think? > > > > > > > > > > > > > > > > > > > > Cheers, > > > > > > > > > > > > > > > > > > > > Paul > > > > > > > > > > > > > > > > > > > > [0]: https://lkml.org/lkml/2019/3/6/82 > > > > > > > > > > [1]: https://patchwork.linuxtv.org/patch/55947/ > > > > > > > > > > [2]: > > > > > > > > > > https://chromium.googlesource.com/chromiumos/third_party/ke > > > > > > > > > > rnel/+/4d7cb46539a93bb6acc802f5a46acddb5aaab378 > > >
