linux-kernel - arm: Optimization for ethernet MAC handling at91

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Message-ID: <3DBBD805E3BA064A87F551C0E8BD3674028973F5@MAILSRV.intcomgrp.com>
Date:	Tue, 12 Jan 2010 10:39:25 -0500
From:	"James Kosin" <JKosin@...comgrp.com>
To:	<linux-kernel@...r.kernel.org>
Subject: arm: Optimization for ethernet MAC handling at91_ether.c

Everyone,

Since, a AT91_EMAC_TUND only happens when the transmitter is unable to
transfer the frame in time for a frame to be sent.  It makes sense to
RETRY the packet in this condition in the ISR.
Or would this overcomplicate a simple task?
                ... see below ...

James

---- code snippet ----

/*
 * MAC interrupt handler
 */
static irqreturn_t at91ether_interrupt(int irq, void *dev_id) { ...

                if (intstatus & AT91_EMAC_TCOM) {       /* Transmit
complete */
                                /* The TCOM bit is set even if the
transmission failed. */
                                if (intstatus & (AT91_EMAC_TUND |
AT91_EMAC_RTRY))
                                                dev->stats.tx_errors +=
1;

                                if (lp->skb) {
 
dev_kfree_skb_irq(lp->skb);
                                                lp->skb = NULL;
                                                dma_unmap_single(NULL,
lp->skb_physaddr, lp->skb_length, DMA_TO_DEVICE);
                                }
                                netif_wake_queue(dev);
                }
...

---- Alternate approach ----

                                /* The TCOM bit is set even if the
transmission failed. */
                                if (intstatus & (AT91_EMAC_TUND)) {
                                                /* Set address of the
data in the Transmit Address register */
 
at91_emac_write(AT91_EMAC_TAR, lp->skb_physaddr);
                                                /* Set length of the
packet in the Transmit Control register */
 
at91_emac_write(AT91_EMAC_TCR, skb->len);
                                }
                                else if (intstatus & (AT91_EMAC_RTRY))
                                                dev->stats.tx_errors +=
1;

...
I do know there needs to be a bit more code then to handle the
successful case below this; but, this is enough to understand what I am
talking about.  The UNDERRUN error should happen infrequently and in
ideal circumstances not happen at all.
 
 


----
James Kosin
Software Engineer
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