netdev:bfin_mac: reclaim and free tx skb as soon as possible after transfer

SKBs hold onto resources that can't be held indefinitely, such as TCP
socket references and netfilter conntrack state.  So if a packet is left
in TX ring for a long time, there might be a TCP socket that cannot be
closed and freed up.

Current blackfin EMAC driver always reclaim and free used tx skbs in future
transfers. The problem is that future transfer may not come as soon as
possible. This patch start a timer after transfer to reclaim and free skb.
There is nearly no performance drop with this patch.

TX interrupt is not enabled because of a strange behavior of the Blackfin EMAC.
If EMAC TX transfer control is turned on, endless TX interrupts are triggered
no matter if TX DMA is enabled or not. Since DMA walks down the ring automatically,
TX transfer control can't be turned off in the middle. The only way is to disable
TX interrupt completely.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/net/bfin_mac.h b/drivers/net/bfin_mac.h
index 1ae7b82ceeee..04e4050df18b 100644
--- a/drivers/net/bfin_mac.h
+++ b/drivers/net/bfin_mac.h
@@ -13,9 +13,12 @@
 #include <linux/net_tstamp.h>
 #include <linux/clocksource.h>
 #include <linux/timecompare.h>
+#include <linux/timer.h>
 
 #define BFIN_MAC_CSUM_OFFLOAD
 
+#define TX_RECLAIM_JIFFIES (HZ / 5)
+
 struct dma_descriptor {
         struct dma_descriptor *next_dma_desc;
         unsigned long start_addr;
@@ -68,6 +71,8 @@ struct bfin_mac_local {
 
         int wol;                /* Wake On Lan */
         int irq_wake_requested;
+        struct timer_list tx_reclaim_timer;
+        struct net_device *ndev;
 
         /* MII and PHY stuffs */
         int old_link;          /* used by bf537_adjust_link */