linux-kernel - Re: 64-bit DMA problems with BCM4312 using b43

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Message-ID: <4AFE26C5.5080402@lwfinger.net>
Date:	Fri, 13 Nov 2009 21:40:53 -0600
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Matthew Garrett <mjg59@...f.ucam.org>
CC:	Michael Buesch <mb@...sch.de>, bcm43xx-dev@...ts.berlios.de,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 64-bit DMA problems with BCM4312 using b43

On 11/13/2009 03:13 PM, Matthew Garrett wrote:
> On Fri, Nov 13, 2009 at 03:05:18PM -0600, Larry Finger wrote:
> 
>> I'm in the process of creating a patch to set the latency to 200 usec. The
>> default is 2000. On my fast prosessors, it should not be anything nearly that
>> slow. If we determine this to be the problem, then we can try tuning.
> 
> The latency is the amount of time it takes to get out of deep C states 
> and into C0. That's a function of the processor design rather than the 
> frequency.

Thanks for your suggestion. The value of 200 fixed one of the two machines and
greatly improved the other. He is currently testing with a value of 150, and
will try 100 if that still fails.

Larry


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