netdev - Re: linux-2..6.33-rc7 and b43

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Date:	Sun, 14 Feb 2010 19:59:54 +0100
From:	Gábor Stefanik <netrolller.3d@...il.com>
To:	Thomas Backlund <tmb@...driva.org>
Cc:	Larry Finger <Larry.Finger@...inger.net>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: linux-2..6.33-rc7 and b43

On Sun, Feb 14, 2010 at 7:44 PM, Thomas Backlund <tmb@...driva.org> wrote:
> Larry Finger skrev 14.2.2010 18:36:
>>
>> On 02/14/2010 03:53 AM, Thomas Backlund wrote:
>>>
>>> Hi,
>>> (please cc me on replies)
>>>
>>> We have a user that tried out b43, but got this in the logs:
>>>
>>> --- cut ---
>>> 65858:Feb  9 22:05:16 elmo kernel: b43-phy2 ERROR: This device does not
>>> support DMA on your system. Please use PIO instead. 65859:Feb  9
>>> 22:05:16 elmo kernel: b43-phy2 ERROR: CONFIG_B43_FORCE_PIO must
>>> be set in your kernel configuration.
>>> 65860:Feb  9 22:05:16 elmo kernel: b43-phy2 debug: Adding Interface type
>>> 2
>>> 65861:Feb  9 22:05:16 elmo kernel: b43-phy2 ERROR: Fatal DMA error:
>>> 0x00000400, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000
>>>
>>> 65862:Feb  9 22:05:16 elmo kernel: b43-phy2 ERROR: This device does not
>>> support DMA on your system. Please use PIO instead.
>>> 65863:Feb  9 22:05:16 elmo kernel: b43-phy2 ERROR: CONFIG_B43_FORCE_PIO
>>> must be set in your kernel configuration.
>>> --- cut ---
>>>
>>>
>>>
>>> But reading the Kconfig help, it states:
>>> --- cut ---
>>> config B43_FORCE_PIO
>>>         bool "Force usage of PIO instead of DMA"
>>>         depends on B43&&  B43_DEBUG
>>>         ---help---
>>>           This will disable DMA and always enable PIO instead.
>>>
>>>           Say N!
>>>           This is only for debugging the PIO engine code. You do
>>>           _NOT_ want to enable this.
>>> --- cut ---
>>>
>>>
>>> So,
>>> wich one is it ?
>>>
>>> Do I belive the dmesg output, or the Kconfig ?
>>>
>>> Note,
>>> the b43 works for the user if he enable the CONFIG_B43_FORCE_PIO.
>>>
>>> But I'm thinking of this problem from a distro point of view.
>>> Will it break for others if I enable it ?
>>
>>> From a distro point of view, you would not want to set FORCE_PIO as the
>>
>> performance penalty would be very large.
>>
>
> As I suspected.
> Thanks for confirming it.
>
>> You do not give the specific details on the problem system; however, it is
>> probably a BCM4312 802.11 b/g device with PCI ID 14e4:4315 being used with
>> an
>> Atom processor in a netbook. We have no fix.
>>
>
> Sorry about the missing info...
> I asked a few times from the user, and got no reponse until today a few
> hours after your response...
>
> It is indeed a BCM4312 802.11 b/g device with PCI ID 14e4:4315 on a Dell
> laptop with a Intel ICH9M series chipset and a Intel Core(TM)2 Duo CPU T7250
> @ 2.00GHz.

Weird... that's not an Intel Atom, but a Core 2 Duo, standard-voltage.
Mind posting any more details on this system?

>
>> In the 2.6.34 code, b43 will be changed to allow the selection of PIO mode
>> at
>> run time rather than compile time. For a distro, this method is clearly
>> superior. Those users that need PIO can select it without forcing the
>> performance penalty on everyone. The patch was too late for the 2.6.33
>> merge,
>> and too intrusive to be applied to 2.6.33-rcX. It has been present in the
>> wireless-testing code base for 2 months with no trouble reported, thus it
>> should
>> be safe for inclusion in your kernels. The relevant patch is attached.
>>
>
> Nice solution.
>
> What about making it autodetected ?
> Or is it only a "last resort" with the hopes of getting the issue fixed?
>
> Anyway, thanks for the patch.
>
> --
> Thomas
> --
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