Re: [PATCH 1/8] [I/OAT] DMA memcpy subsystem

[Kumar Gala <galak@kernel.crashing.org>]

On Mar 28, 2006, at 12:44 PM, Andrew Grover wrote:

> On 3/16/06, Kumar Gala <galak@kernel.crashing.org> wrote:
> > It would seem that when a client registers (or shortly there after
> > when they call dma_async_client_chan_request()) they would expect to
> > get the number of channels they need by some given time period.
> >
> > For example, lets say a client registers but no dma device exists.
> > They will never get called to be aware of this condition.
> >
> > I would think most clients would either spin until they have all the
> > channels they need or fall back to a non-async mechanism.
>
> Clients *are* expected to fall back to non-async if they are not given
> channels. The reason it was implemented with callbacks for
> added/removed was that the client may be initializing before the
> channels are enumerated. For example, the net subsystem will ask for
> channels and not get them for a while, until the ioatdma PCI device is
> found and its driver loads. In this scenario, we'd like the net
> subsystem to be given these channels, instead of them going unused.

Fair, I need to think on that a little more.

> > Also, what do you think about adding an operation type (MEMCPY, XOR,
> > CRYPTO_AES, etc).  We can than validate if the operation type
> > expected is supported by the devices that exist.
>
> No objections, but this speculative support doesn't need to be in our
> initial patchset.

I don't consider it speculative.  The patch is for a generic DMA  
engine interface.  That interface should encompass all users.  I have  
a security/crypto DMA engine that I'd like to front with the generic  
DMA interface today.  Also, I believe there is another Intel group  
with an XOR engine that had a similar concept called ADMA posted a  
while ago.

http://marc.theaimsgroup.com/?t=112603120100004&r=1&w=2

> > Shouldn't we also have a dma_async_client_chan_free()?
>
> Well we could just define it to be chan_request(0) but it doesn't seem
> to be needed. Also, the allocation mechanism we have for channels is
> different from alloc/free's semantics, so it may be best to not muddy
> the water in this area.

Can you explain what the semantics are.

It's been a little while since I posted so my thoughts on the subject  
are going to take a little while to come back to me :)

- kumar
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