Re: [PATCH] dmaengine: qcom_bam_dma: Add descriptor flag APIs

[Srinivas Kandagatla]

On 22/05/14 16:32, Andy Gross wrote:
> On Thu, May 22, 2014 at 04:27:05PM +0100, Srinivas Kandagatla wrote:
>
> <snip>
>
> > > The EOT is not used for every transaction.  It is part of a handshaking
> > > protocol with the attached peripheral, much like the NWD (notify when done).  As
> > > near as I can tell today, no peripheral depends on the EOB, so we could drop it
> > > for now until it is needed and cross this bridge when we need to.
> >
> > As EOT behaviour is totally dependent on the attached peripheral(or
> > channel), Can't we make this specific to channel by passing
> > additional flags in the DT dma channel descriptors? This will be
> > better abstraction for drivers as well.
>
> Even for channels where you want to use EOT, you don't use it for every
> transaction.  So a global channel flag isn't going to work.  This is the same
> for NWD.  It is a per descriptor choice.

Thanks Andy for explaining, I got it now.
> > I know that EOT flag is part of descriptor but still some channels
> > *must* have EOT to run there state-machine correctly. So making it
> > optional for those channels might be wrong.
> >
> > Are there any use cases for particular *channel* where EOT
> > requirement changes dynamically?
>
> I2C is one example.  You place EOT on the last transaction that makes up a
> write/read transaction.  You may have multiple descriptors to send data, but the
> last one has EOT.  And for read transactions, you place NWD on the last read
> transaction.
>
> <snip>
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