Re: [RFR] gianfar ethernet driver

[Jeff Garzik <jgarzik@xxxxxxxxx>]

On Tue, Jul 06, 2004 at 11:18:02PM -0400, jamal wrote:
> You dont return a 1 anywhere.

That OK in one model.


> Heres what i mean (substitute your code):
> if no more descriptors
> netif_stop_queue(dev)
> unlock
> return 1
> process packet and stash on ring
> return 0

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.

        Jeff