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[netdrvr e100] experiment with doing RX in a similar manner to eepro100
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I was going to say that eepro100's speedo_rx_link() does the same DMA
abuse as e100, but then I noticed one little detail: eepro100 sets  both
EL (end of list) and S (suspend) bits in the RFD as it chains it  to the
RFD list.  e100 was only setting the EL bit.  Hmmm, that's  interesting.
That means that if HW reads a RFD with the S-bit set,  it'll process
that RFD and then suspend the receive unit.  The  receive unit will
resume when SW clears the S-bit.  There is no need  for SW to restart
the receive unit.  Which means a lot of the receive  unit state tracking
code in the driver goes away.

So here's a patch against 2.6.14.  (Sorry for inlining it; the mailer
I'm using now will mess with the word wrap).  I can't test this on
XScale (unless someone has an e100 module for Gumstix :) .  It should
be doing exactly what eepro100 does with RFDs.  I don't believe this
change will introduce a performance hit because the S-bit and EL-bit  go
hand-in-hand meaning if we're going to suspend because of the S- bit,
we're on the last resource anyway, so we'll have to wait for SW  to
replenish.
(cherry picked from 29e79da9495261119e3b2e4e7c72507348e75976 commit)
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Scott Feldman authored and Jeff Garzik committed Apr 28, 2007
1 parent 2933d42 commit d52df4a
Showing 1 changed file with 9 additions and 63 deletions.
72 changes: 9 additions & 63 deletions drivers/net/e100.c
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Original file line number Diff line number Diff line change
Expand Up @@ -282,12 +282,6 @@ enum scb_status {
rus_mask = 0x3C,
};

enum ru_state {
RU_SUSPENDED = 0,
RU_RUNNING = 1,
RU_UNINITIALIZED = -1,
};

enum scb_stat_ack {
stat_ack_not_ours = 0x00,
stat_ack_sw_gen = 0x04,
Expand Down Expand Up @@ -529,7 +523,6 @@ struct nic {
struct rx *rx_to_use;
struct rx *rx_to_clean;
struct rfd blank_rfd;
enum ru_state ru_running;

spinlock_t cb_lock ____cacheline_aligned;
spinlock_t cmd_lock;
Expand Down Expand Up @@ -951,7 +944,7 @@ static void e100_get_defaults(struct nic *nic)
((nic->mac >= mac_82558_D101_A4) ? cb_cid : cb_i));

/* Template for a freshly allocated RFD */
nic->blank_rfd.command = cpu_to_le16(cb_el);
nic->blank_rfd.command = cpu_to_le16(cb_el & cb_s);
nic->blank_rfd.rbd = 0xFFFFFFFF;
nic->blank_rfd.size = cpu_to_le16(VLAN_ETH_FRAME_LEN);

Expand Down Expand Up @@ -1746,19 +1739,11 @@ static int e100_alloc_cbs(struct nic *nic)
return 0;
}

static inline void e100_start_receiver(struct nic *nic, struct rx *rx)
static inline void e100_start_receiver(struct nic *nic)
{
if(!nic->rxs) return;
if(RU_SUSPENDED != nic->ru_running) return;

/* handle init time starts */
if(!rx) rx = nic->rxs;

/* (Re)start RU if suspended or idle and RFA is non-NULL */
if(rx->skb) {
e100_exec_cmd(nic, ruc_start, rx->dma_addr);
nic->ru_running = RU_RUNNING;
}
/* Start if RFA is non-NULL */
if(nic->rx_to_clean->skb)
e100_exec_cmd(nic, ruc_start, nic->rx_to_clean->dma_addr);
}

#define RFD_BUF_LEN (sizeof(struct rfd) + VLAN_ETH_FRAME_LEN)
Expand Down Expand Up @@ -1787,7 +1772,7 @@ static int e100_rx_alloc_skb(struct nic *nic, struct rx *rx)
put_unaligned(cpu_to_le32(rx->dma_addr),
(u32 *)&prev_rfd->link);
wmb();
prev_rfd->command &= ~cpu_to_le16(cb_el);
prev_rfd->command &= ~cpu_to_le16(cb_el & cb_s);
pci_dma_sync_single_for_device(nic->pdev, rx->prev->dma_addr,
sizeof(struct rfd), PCI_DMA_TODEVICE);
}
Expand Down Expand Up @@ -1825,10 +1810,6 @@ static int e100_rx_indicate(struct nic *nic, struct rx *rx,
pci_unmap_single(nic->pdev, rx->dma_addr,
RFD_BUF_LEN, PCI_DMA_FROMDEVICE);

/* this allows for a fast restart without re-enabling interrupts */
if(le16_to_cpu(rfd->command) & cb_el)
nic->ru_running = RU_SUSPENDED;

/* Pull off the RFD and put the actual data (minus eth hdr) */
skb_reserve(skb, sizeof(struct rfd));
skb_put(skb, actual_size);
Expand Down Expand Up @@ -1859,54 +1840,25 @@ static void e100_rx_clean(struct nic *nic, unsigned int *work_done,
unsigned int work_to_do)
{
struct rx *rx;
int restart_required = 0;
struct rx *rx_to_start = NULL;

/* are we already rnr? then pay attention!!! this ensures that
* the state machine progression never allows a start with a
* partially cleaned list, avoiding a race between hardware
* and rx_to_clean when in NAPI mode */
if(RU_SUSPENDED == nic->ru_running)
restart_required = 1;

/* Indicate newly arrived packets */
for(rx = nic->rx_to_clean; rx->skb; rx = nic->rx_to_clean = rx->next) {
int err = e100_rx_indicate(nic, rx, work_done, work_to_do);
if(-EAGAIN == err) {
/* hit quota so have more work to do, restart once
* cleanup is complete */
restart_required = 0;
break;
} else if(-ENODATA == err)
if(e100_rx_indicate(nic, rx, work_done, work_to_do))
break; /* No more to clean */
}

/* save our starting point as the place we'll restart the receiver */
if(restart_required)
rx_to_start = nic->rx_to_clean;

/* Alloc new skbs to refill list */
for(rx = nic->rx_to_use; !rx->skb; rx = nic->rx_to_use = rx->next) {
if(unlikely(e100_rx_alloc_skb(nic, rx)))
break; /* Better luck next time (see watchdog) */
}

if(restart_required) {
// ack the rnr?
writeb(stat_ack_rnr, &nic->csr->scb.stat_ack);
e100_start_receiver(nic, rx_to_start);
if(work_done)
(*work_done)++;
}
}

static void e100_rx_clean_list(struct nic *nic)
{
struct rx *rx;
unsigned int i, count = nic->params.rfds.count;

nic->ru_running = RU_UNINITIALIZED;

if(nic->rxs) {
for(rx = nic->rxs, i = 0; i < count; rx++, i++) {
if(rx->skb) {
Expand All @@ -1928,7 +1880,6 @@ static int e100_rx_alloc_list(struct nic *nic)
unsigned int i, count = nic->params.rfds.count;

nic->rx_to_use = nic->rx_to_clean = NULL;
nic->ru_running = RU_UNINITIALIZED;

if(!(nic->rxs = kcalloc(count, sizeof(struct rx), GFP_ATOMIC)))
return -ENOMEM;
Expand All @@ -1943,7 +1894,6 @@ static int e100_rx_alloc_list(struct nic *nic)
}

nic->rx_to_use = nic->rx_to_clean = nic->rxs;
nic->ru_running = RU_SUSPENDED;

return 0;
}
Expand All @@ -1963,10 +1913,6 @@ static irqreturn_t e100_intr(int irq, void *dev_id)
/* Ack interrupt(s) */
writeb(stat_ack, &nic->csr->scb.stat_ack);

/* We hit Receive No Resource (RNR); restart RU after cleaning */
if(stat_ack & stat_ack_rnr)
nic->ru_running = RU_SUSPENDED;

if(likely(netif_rx_schedule_prep(netdev))) {
e100_disable_irq(nic);
__netif_rx_schedule(netdev);
Expand Down Expand Up @@ -2058,7 +2004,7 @@ static int e100_up(struct nic *nic)
if((err = e100_hw_init(nic)))
goto err_clean_cbs;
e100_set_multicast_list(nic->netdev);
e100_start_receiver(nic, NULL);
e100_start_receiver(nic);
mod_timer(&nic->watchdog, jiffies);
if((err = request_irq(nic->pdev->irq, e100_intr, IRQF_SHARED,
nic->netdev->name, nic->netdev)))
Expand Down Expand Up @@ -2139,7 +2085,7 @@ static int e100_loopback_test(struct nic *nic, enum loopback loopback_mode)
mdio_write(nic->netdev, nic->mii.phy_id, MII_BMCR,
BMCR_LOOPBACK);

e100_start_receiver(nic, NULL);
e100_start_receiver(nic);

if(!(skb = netdev_alloc_skb(nic->netdev, ETH_DATA_LEN))) {
err = -ENOMEM;
Expand Down

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