Re: [PATCH] [RFC] dmaengine: add fifo_size member

[Jon Hunter]

On 06/06/2019 17:44, Dmitry Osipenko wrote:
> 06.06.2019 19:32, Jon Hunter ÐÐÑÐÑ:
>>
>> On 06/06/2019 16:18, Dmitry Osipenko wrote:
>>
>> ...
>>
>>>>> If I understood everything correctly, the FIFO buffer is shared among
>>>>> all of the ADMA clients and hence it should be up to the ADMA driver to
>>>>> manage the quotas of the clients. So if there is only one client that
>>>>> uses ADMA at a time, then this client will get a whole FIFO buffer, but
>>>>> once another client starts to use ADMA, then the ADMA driver will have
>>>>> to reconfigure hardware to split the quotas.
>>>>
>>>> The FIFO quotas are managed by the ADMAIF driver (does not exist in
>>>> mainline currently but we are working to upstream this) because it is
>>>> this device that owns and needs to configure the FIFOs. So it is really
>>>> a means to pass the information from the ADMAIF to the ADMA.
>>>
>>> So you'd want to reserve a larger FIFO for an audio channel that has a
>>> higher audio rate since it will perform reads more often. You could also
>>> prioritize one channel over the others, like in a case of audio call for
>>> example.
>>>
>>> Is the shared buffer smaller than may be needed by clients in a worst
>>> case scenario? If you could split the quotas statically such that each
>>> client won't ever starve, then seems there is no much need in the
>>> dynamic configuration.
>>
>> Actually, this is still very much relevant for the static case. Even if
>> we defined a static configuration of the FIFO mapping in the ADMAIF
>> driver we still need to pass this information to the ADMA. I don't
>> really like the idea of having it statically defined in two different
>> drivers.
> 
> Ah, so you need to apply the same configuration in two places. Correct?
> 
> Are ADMAIF and ADMA really two different hardware blocks? Or you
> artificially decoupled the ADMA driver?

These are two different hardware modules with their own register sets.
Yes otherwise, it would be a lot simpler!

Jon

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