> On 4. 10. 2023, at 15:32, Martin Povišer <[email protected]> wrote:
>
>
> Hello Vinod,
>
> some of those things we have discussed on v1 already, let me link
> that here:
> https://lore.kernel.org/asahi/[email protected]/T/#t
>
> Anyway find my replies below.
>
> Best regards, Martin
>
>> On 4. 10. 2023, at 15:12, Vinod Koul <[email protected]> wrote:
>>
>> On 28-08-23, 19:00, Martin Povišer wrote:
>>> Add a dmaengine driver for the Apple SIO coprocessor found on Apple
>>> SoCs where it provides DMA services. Have the driver support cyclic
>>> transactions so that ALSA drivers can rely on it in audio output to
>>> HDMI and DisplayPort.
>>>
>>> Signed-off-by: Martin Povišer <[email protected]>
>>> ---
>>> MAINTAINERS | 2 +
>>> drivers/dma/Kconfig | 11 +
>>> drivers/dma/Makefile | 1 +
>>> drivers/dma/apple-sio.c | 868 ++++++++++++++++++++++++++++++++++++++++
>>> 4 files changed, 882 insertions(+)
>>> create mode 100644 drivers/dma/apple-sio.c
...
>>> +/*
>>> + * There are two kinds of 'transaction descriptors' in play here.
>>> + *
>>> + * There's the struct sio_tx, and the struct dma_async_tx_descriptor embedded
>>> + * inside, which jointly represent a transaction to the dmaengine subsystem.
>>> + * At this time we only support those transactions to be cyclic.
>>> + *
>>> + * Then there are the coprocessor descriptors, which is what the coprocessor
>>> + * knows and understands. These don't seem to have a cyclic regime, so we can't
>>> + * map the dmaengine transaction on an exact coprocessor counterpart. Instead
>>> + * we continually queue up many coprocessor descriptors to implement a cyclic
>>> + * transaction.
>>> + *
>>> + * The number below is the maximum of how far ahead (how many) coprocessor
>>> + * descriptors we should be queuing up, per channel, for a cyclic transaction.
>>> + * Basically it's a made-up number.
>>> + */
>>> +#define SIO_MAX_NINFLIGHT 4
>>
>> you meant SIO_MAX_INFLIGHT if not what is NINFLIGHT?
>
> I mean the number is arbitrary, it doesn’t reflect any coprocessor limit since
> I haven’t run the tests to figure one out. It's supposed to be a small reasonable
> number.
Ah I didn’t get what you were commenting on at first. Sure, INFLIGHT, NINFLIGHT,
it’s the same thing to me. I have a tendency to put in the N to signify it’s
the “number of”.
Best,
Martin