Re: [very-RFC 0/8] TSN driver for the kernel

Henrik Austad
2016-06-12T08:28:58Z

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On Sun, Jun 12, 2016 at 12:38:36PM +0900, Takashi Sakamoto wrote:
> Hi,
>
> I'm one of maintainers for ALSA firewire stack, which handles IEC
> 61883-1/6 and vendor-unique packets on IEEE 1394 bus for consumer
> recording equipments.
> (I'm not in MAINTAINERS because I'm a shy boy.)
>
> IEC 61883-6 describes that one packet can multiplex several types of
> data in its data channels; i.e. Multi Bit Linear Audio data (PCM
> samples), One Bit Audio Data (DSD), MIDI messages and so on.

Hmm, that I did not know, not sure how that applies to AVB, but definately
something I have to look into.

> If you handles packet payload in 'struct snd_pcm_ops.copy', a process
> context of an ALSA PCM applications performs the work. Thus, no chances
> to multiplex data with the other types.

Hmm, ok, I didn't know that, that is something I need to look into -and
incidentally one of the reasons why I posted the series now instead of a
few more months down the road - thanks!

The driver is not adhering fully to any standards right now, the amount of
detail is quite high - but I'm slowly improving as I go through the
standards. Getting on top of all the standards and all the different
subsystems are definately a work in progress (it's a lot to digest!)

> To prevent this situation, current ALSA firewire stack handles packet
> payload in software interrupt context of isochronous context of OHCI
> 1394. As a result of this, the software stack supports PCM substreams
> and MIDI substreams.
>
> In your patcset, there's no actual codes about how to handle any
> interrupt contexts (software / hardware), how to handle packet payload,
> and so on. Especially, for recent sound subsystem, the timing of
> generating interrupts and which context does what works are important to
> reduce playback/capture latency and power consumption.

See reply in other mail :)

> Of source, your intention of this patchset is to show your early concept
> of TSN feature. Nevertheless, both of explaination and codes are
> important to the other developers who have little knowledges about TSN,
> AVB and AES-64 such as me.

Yes, that is one of the things I aimed for, and also getting feedback on
the overall thinking

> And, I might cooperate to prepare for common IEC 61883 layer. For actual
> codes of ALSA firewire stack, please see mainline kernel code. For
> actual devices of IEC 61883-1/6 and IEEE 1394 bus, please refer to my
> report in 2014. At least, you can get to know what to consider about
> developing upper drivers near ALSA userspace applications.
> https://github.com/takaswie/alsa-firewire-report

Thanks, I'll dig into that, much appreciated

> (But I confirm that the report includes my misunderstandings in clause
> 3.4 and 6.2. need more time...)

ok, good to know

Thank you for your input, very much appreicated!

--
Henrik Austad

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