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

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

On 3/16/06, Kumar Gala [off-list ref] wrote:

quoted

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.

quoted

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

quoted

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