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Date:   Thu, 6 Jun 2019 15:36:03 +0100
From:   Jon Hunter <>
To:     Dmitry Osipenko <>,
        Peter Ujfalusi <>,
        Sameer Pujar <>, Vinod Koul <>
CC:     <>, <>,
        <>, <>,
        <>, <>, <>,
        <>, linux-tegra <>
Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member

On 06/06/2019 15:26, Jon Hunter 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.
>> You could also simply hardcode the quotas per client in the ADMA driver
>> if the quotas are going to be static anyway.
> Essentially this is what we have done so far, but Sameer is looking for
> a way to make this more programmable/flexible. We can always do that if
> there is no other option indeed. However, seems like a good time to see
> if there is a better way.

My thoughts on resolving this, in order of preference, would be ...

1. Add a new 'fifo_size' variable as Sameer is proposing.
2. Update the ADMA driver to use src/dst_maxburst as the fifo size and
   then have the ADMA driver set a suitable burst size for its burst
3. Resort to a static configuration.

I can see that #1 only makes sense if others would find it useful,
otherwise #2, may give us enough flexibility for now.



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