On Wed, 15 May 2024 11:50:52 +0200, Jaroslav Kysela wrote: > > On 15. 05. 24 11:17, Hans Verkuil wrote: > > Hi Jaroslav, > > > > On 5/13/24 13:56, Jaroslav Kysela wrote: > >> On 09. 05. 24 13:13, Jaroslav Kysela wrote: > >>> On 09. 05. 24 12:44, Shengjiu Wang wrote: > >>>>>> mem2mem is just like the decoder in the compress pipeline. which is > >>>>>> one of the components in the pipeline. > >>>>> > >>>>> I was thinking of loopback with endpoints using compress streams, > >>>>> without physical endpoint, something like: > >>>>> > >>>>> compress playback (to feed data from userspace) -> DSP (processing) -> > >>>>> compress capture (send data back to userspace) > >>>>> > >>>>> Unless I'm missing something, you should be able to process data as fast > >>>>> as you can feed it and consume it in such case. > >>>>> > >>>> > >>>> Actually in the beginning I tried this, but it did not work well. > >>>> ALSA needs time control for playback and capture, playback and capture > >>>> needs to synchronize. Usually the playback and capture pipeline is > >>>> independent in ALSA design, but in this case, the playback and capture > >>>> should synchronize, they are not independent. > >>> > >>> The core compress API core no strict timing constraints. You can eventually0 > >>> have two half-duplex compress devices, if you like to have really independent > >>> mechanism. If something is missing in API, you can extend this API (like to > >>> inform the user space that it's a producer/consumer processing without any > >>> relation to the real time). I like this idea. > >> > >> I was thinking more about this. If I am right, the mentioned use in gstreamer > >> is supposed to run the conversion (DSP) job in "one shot" (can be handled > >> using one system call like blocking ioctl). The goal is just to offload the > >> CPU work to the DSP (co-processor). If there are no requirements for the > >> queuing, we can implement this ioctl in the compress ALSA API easily using the > >> data management through the dma-buf API. We can eventually define a new > >> direction (enum snd_compr_direction) like SND_COMPRESS_CONVERT or so to allow > >> handle this new data scheme. The API may be extended later on real demand, of > >> course. > >> > >> Otherwise all pieces are already in the current ALSA compress API > >> (capabilities, params, enumeration). The realtime controls may be created > >> using ALSA control API. > > > > So does this mean that Shengjiu should attempt to use this ALSA approach first? > > I've not seen any argument to use v4l2 mem2mem buffer scheme for this > data conversion forcefully. It looks like a simple job and ALSA APIs > may be extended for this simple purpose. > > Shengjiu, what are your requirements for gstreamer support? Would be a > new blocking ioctl enough for the initial support in the compress ALSA > API? If it works with compress API, it'd be great, yeah. So, your idea is to open compress-offload devices for read and write, then and let them convert a la batch jobs without timing control? For full-duplex usages, we might need some more extensions, so that both read and write parameters can be synchronized. (So far the compress stream is a unidirectional, and the runtime buffer for a single stream.) And the buffer management is based on the fixed size fragments. I hope this doesn't matter much for the intended operation? thanks, Takashi
