netdev - RE: [PATCH v1 1/1 net] net: fec: workaround stop tx during errata ERR006358

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Date:	Thu, 25 Jul 2013 08:16:23 +0000
From:	Duan Fugang-B38611 <B38611@...escale.com>
To:	Li Frank-B20596 <B20596@...escale.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"l.stach@...gutronix.de" <l.stach@...gutronix.de>,
	"r.schwebel@...gutronix.de" <r.schwebel@...gutronix.de>,
	"lznuaa@...il.com" <lznuaa@...il.com>
Subject: RE: [PATCH v1 1/1 net] net: fec: workaround stop tx during errata
 ERR006358

On 25/07/13 14:06, Li Frank wrote:
>If the ready bit in the transmit buffer descriptor (TxBD[R]) is previously detected as not set during a prior frame transmission, then the ENET_TDAR[TDAR] bit is cleared at a later time, even if additional TxBDs were added to the ring and the ENET_TDAR[TDAR] bit is set. This results in frames not being transmitted until there is a 0-to-1 transition on ENET_TDAR[TDAR].
>
>Workarounds:
>code can use the transmit frame interrupt flag (ENET_EIR[TXF]) as a method to detect whether the ENET has completed transmission and the ENET_TDAR[TDAR] has been cleared. If ENET_TDAR[TDAR] is detected as cleared when packets are queued and waiting for transmit, then a write to the TDAR bit will restart TxBD processing.
>
>This case main happen when loading is light. A ethernet package may not send out utile next package put into tx queue.
>
>How to test:
>while [ true ]
>do
>	ping <IP> -s 10000 -w 4
>	ping <IP> -s 6000 -w 2
>	ping <IP> -s 4000 -w 2
>	ping <IP> -s 10000 -w 2
>done
>
>You will see below result in overnight test.
>
>6008 bytes from 10.192.242.116: seq=1 ttl=128 time=0.722 ms
>4008 bytes from 10.192.242.116: seq=0 ttl=128 time=1001.008 ms
>4008 bytes from 10.192.242.116: seq=1 ttl=128 time=1.010 ms
>10008 bytes from 10.192.242.116: seq=0 ttl=128 time=0.896 ms
>
>After apply this patch, >1000ms delay disappear.
>
>Signed-off-by: Frank Li <Frank.Li@...escale.com>

Acked-by: Fugang Duan  <B38611@...escale.com>

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