netdev - Re: b44: Reset due to FIFO overflow.

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Date:	Mon, 28 Jun 2010 02:33:26 -0700
From:	Mitchell Erblich <erblichs@...thlink.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	James Courtier-Dutton <james.dutton@...il.com>,
	netdev@...r.kernel.org
Subject: Re: b44: Reset due to FIFO overflow.


On Jun 28, 2010, at 2:13 AM, Eric Dumazet wrote:

> Le lundi 28 juin 2010 à 08:41 +0100, James Courtier-Dutton a écrit :
>> Hi,
>> 
>> Reference:
>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/279102
>> 
>> I can see this bug and can reproduce it 100% on demand.
>> The problem seems to be that when the b44 has a incoming FIFO buffer
>> overflow, it resets the entire card, dis-associates with the access
>> point and therefore takes some time before it can pass traffic again.
>> Can anyone point me to some code that would just recover the FIFO
>> instead of reset the entire card?
>> 
>> I am a kernel developer, but I don't have any data sheets on this card
>> so was hoping someone with more knowledge of its workings, could help
>> me.
>> 
>> I can then test it, and see if it is a good fix or not.
>> 
> 
> Hi
> 
> Problem is we dont know if a Receive Fifo overflow is a minor or major
> indication from b44 chip.
> 
> A minor indication would be : Chip tells us one or more frame were lost.
> No special action needed from driver.
> 
> A major indication (as of current implemented in b44 driver) is :
> I am completely out of order and need a reset. Please do it.
> 
> Patch to switch from major to minor indication is easy, but we dont know
> if its valid or not.
> 
> diff --git a/drivers/net/b44.h b/drivers/net/b44.h
> index e1905a4..514dc3a 100644
> --- a/drivers/net/b44.h
> +++ b/drivers/net/b44.h
> @@ -42,7 +42,7 @@
> #define  ISTAT_EMAC		0x04000000 /* EMAC Interrupt */
> #define  ISTAT_MII_WRITE	0x08000000 /* MII Write Interrupt */
> #define  ISTAT_MII_READ		0x10000000 /* MII Read Interrupt */
> -#define  ISTAT_ERRORS (ISTAT_DSCE|ISTAT_DATAE|ISTAT_DPE|ISTAT_RDU|ISTAT_RFO|ISTAT_TFU)
> +#define  ISTAT_ERRORS (ISTAT_DSCE|ISTAT_DATAE|ISTAT_DPE|ISTAT_RDU|ISTAT_TFU)
> #define B44_IMASK	0x0024UL /* Interrupt Mask */
> #define  IMASK_DEF		(ISTAT_ERRORS | ISTAT_TO | ISTAT_RX | ISTAT_TX)
> #define B44_GPTIMER	0x0028UL /* General Purpose Timer */
> 
> --
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Why wouldn't the ability to recv frames after a Recv FIFO overflow
 indicate that a reset is NOT required?

Thus,  should't it be an indication of congestion if associated with a single
flow and either speed up (reduce latency to service) the recv side or 
slow down the xmit side?

Mitchell Erblich--
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