linux-kernel - Re: [PATCH] [RFC] dmaengine: add fifo

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Date:   Thu, 6 Jun 2019 19:44:41 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Sameer Pujar <spujar@...dia.com>, Vinod Koul <vkoul@...nel.org>
Cc:     dan.j.williams@...el.com, tiwai@...e.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        sharadg@...dia.com, rlokhande@...dia.com, dramesh@...dia.com,
        mkumard@...dia.com, linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member

06.06.2019 19:32, Jon Hunter пишет:
> 
> 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?