On Tue, 2004-07-06 at 23:29, Jeff Garzik wrote:

On Tue, Jul 06, 2004 at 11:18:02PM -0400, jamal wrote:

quoted

You dont return a 1 anywhere.

That OK in one model.

True returning 0 this is not wrong; it
results in an extra call in the layer above the driver.
(I was trying to point that out in earlier email)

When you are not dealing with fragments, the most optimal model
eliminates the overflow case completely, so your ->hard_start_xmit looks
like

	lock
	queue packet to DMA ring
	if (DMA ring full)
		netif_stop_queue()
	unlock

	return 0

If you can be sure -- by design -- that room is always available when
the queue is not stopped, then that's fine.

With fragments, you cannot be sure of this, if you do not wish to
reserve MY_HW_MAX_FRAGMENTS slots on the DMA.  Such a case would require
moving the "if no more descriptors" check up, and returning 1 when the
ring is empty.

But ideally, you should write the driver where such a condition does not
occur at all.

Ok, I overlooked fragments. I think it would be useful to capture this
in the doc you were preping. BTW, why can you figure out the fragment
count? If you can then the check for number of descriptors availabel
could account for that.

cheers,
jamal