On Wed, 22 May 2019 09:29:24 +0200 Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote: > On Wed, 22 May 2019 15:39:37 +0900 > Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote: > > > > It would be premature to state that we are excluding. We are just > > > trying to find one format to get things upstream, and make sure we have > > > a plan how to extend it. Trying to support everything on the first try > > > is not going to work so well. > > > > > > What is interesting to provide is how does you IP achieve multi-slice > > > decoding per frame. That's what we are studying on the RK/Hantro chip. > > > Typical questions are: > > > > > > 1. Do all slices have to be contiguous in memory > > > 2. If 1., do you place start-code, AVC header or pass a seperate index to let the HW locate the start of each NAL ? > > > 3. Does the HW do support single interrupt per frame (RK3288 as an example does not, but RK3399 do) > > > > AFAICT, the bit about RK3288 isn't true. At least in our downstream > > driver that was created mostly by RK themselves, we've been assuming > > that the interrupt is for the complete frame, without any problems. > > I confirm that's what happens when all slices forming a frame are packed > in a single output buffer: you only get one interrupt at the end of the > decoding process (in that case, when the frame is decoded). Of course, > if you split things up and do per-slice decoding instead (one slice per > buffer) you get an interrupt per slice, though I didn't manage to make > that work. > I get a DEC_BUFFER interrupt (AKA, "buffer is empty but frame is not > fully decoded") on the first slice and an ASO (Arbitrary Slice Ordering) > interrupt on the second slice, which makes me think some states are > reset between the 2 operations leading the engine to think that the > second slice is part of a new frame. > > Anyway, it doesn't sound like a crazy idea to support both per-slice > and per-frame decoding and maybe have a way to expose what a > specific codec can do (through an extra cap mechanism). > The other option would be to support only per-slice decoding with a > mandatory START_FRAME/END_FRAME sequence to let drivers for HW that > only support per-frame decoding know when they should trigger the > decoding operation. Just to clarify, we can use Hans' V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF work to identify start/end frame boundaries, the only problem I see is that users are not required to clear the flag on the last slice of a frame, so there's no way for the driver to know when it should trigger the decode-frame operation. I guess we could trigger this decode operation when v4l2_m2m_release_capture_buf() returns true, but I wonder if it's not too late to do that. > The downside is that it implies having a bounce > buffer where the driver can pack slices to be decoded on the END_FRAME > event. >
