Re: [PATCH] dmaengine: at_hdmac: new driver for the Atmel AHB DMAController

[Nicolas Ferre]

Dan Williams :
> On Fri, Nov 14, 2008 at 9:34 AM, Nicolas Ferre <nicolas.ferre@xxxxxxxxx> wrote:
> > > >  include/linux/at_hdmac.h                |   26 +
> > > ...this header should be moved somewhere under arch/arm/include.
> > This is where dw_dmac.h resides. Moreover, if one day this IP is implemented
> > on a different architecture, it will be good not to reach it through
> > arch/arm path.
>
> Ok, I won't gate acceptance on this since dw_dmac already set the
> precedent, but shouldn't the header move after the IP has been
> duplicated?  Just my 2cents.

Ok, I follow your advice.


> > > > +               memset(desc, 0, sizeof(struct at_desc));
> > > > +               dma_async_tx_descriptor_init(&desc->txd, chan);
> > > > +               async_tx_ack(&desc->txd);
> > > the DMA_CTRL_ACK bit is under control of the client.  It should be
> > > read-only to the driver (except for extra descriptors that the driver
> > > creates on behalf of the client).
> > This is precisely where the descriptors are been created so, I thought it
> > should be ok to initialize this bit. Am I right ?
>
> They will be acknowledged by client code.  Calls like async_memcpy
> assume that the the ack bit is clear by default so they can specify
> some actions to run at completion time.  By setting it early, at
> descriptor allocation time, async_tx will get confused.

This ack bit is annoying me : I cannot figure out how it is used for 
plain memcopy/slave offload calls...

Moreover, at recycle time, if I keep a descriptor chain as a whole, I 
have to introduce another state for my descriptors : consumed but not 
freed yet (with another linked list management).
If I only take care of the ACK flag for releasing descriptors, I loose 
the dependency in my descriptor chain (in a multi-descriptor memcpy case).

Can I only consider this information without taking care of the chaining 
dependency (and loose this information in a multi-descriptor operation) ?
Or, may I drop this DMA_CTRL_ACK bit management as I do not have the 
usefulness of redoing an operations on one descriptor (no xor engine) ?

Kind regards,
--
Nicolas Ferre

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