[PATCH] b43: A fix for DMA transmission sequence errors

[Rafał Miłecki]

2013/3/23 Rafał Miłecki <zajec5 at gmail.com>:
> 2013/3/23 Chris Vine <chris at cvine.freeserve.co.uk>:
>> On Sat, 23 Mar 2013 11:35:17 +0100
>> Michael Büsch <m at bues.ch> wrote:
>>> On Sat, 23 Mar 2013 00:27:30 +0100
>>> Rafał Miłecki <zajec5 at gmail.com> wrote:
>>>
>>> > Today I've plugged my 14e4:4315 and (unfortunately?) it's working
>>> > pretty well. I hoped to reproduce some problems but failed to do
>>> > so. I was transmitting for an hour with average speed 11MiB/s and
>>> > didn't notice any DMA issues.
>>> >
>>> > I was using iperf with interval of 60 seconds and only 3 results
>>> > showed some problems (8.5MiB/s, 2.5MiB/s, 4.5MiB/s). No
>>> > disconnections however and no DMA errors. I just got "Group
>>> > rekeying completed..." in wpa_supplicant.
>>> >
>>> > So as I can't reproduce this, I can't find any other fix for this
>>> > issue, and there's no reason to stop this workaround. I'll just
>>> > apply it and test over weekend to check for any regressions, but
>>> > they are highly unlikely.
>>>
>>> I don't really believe in this being a firmware bug.
>>>
>>> Some b43 DMA engines (all?) have some alignment and
>>> page-boundary-crossing constraints. I would rather guess that on some
>>> kernels with some options turned on, alignment and/or boundary
>>> constraints are violated every now and then. (and thus the packet
>>> never reaches the firmware).
>>>
>>> I don't remember the details, though. Too long since I worked on that.
>>> But a few sanity checks could probably be added to the code to check
>>> this hypothesis.
>>>
>>> Does the failing kernel/machine have any special things w.r.t. memory?
>>> Like iommu, hugepages, whetever...
>>
>> For what it is worth, this happens to me on both home compiled and
>> distributor kernels (ubuntu and slackware): in fact, any 32-bit kernel
>> that I have tried it on.
>>
>> And it does not happen with the wl driver on the same kernels.  So if
>> this is right, the wl driver must be doing something that the b43 driver
>> does not with respect to alignment: and you might well be right about
>> that.
>
> Could you try changing
> B43_DMA32_RINGMEMSIZE
> from 4096 to 8192 in dma.h?

Blah, ignore that. You're card has 64b DMA, not 32b :|

-- 
Rafał