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Re: [PATCH V3 3.2 2/2] b43: fix DMA on some bugged hardware

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>> Just a side note... Curiously with Intel VT, the b43 driver would start and
work
>> for some short time before it crashed, while the wl proprietary driver (from
>> Broadcom) would not even fully load.
> I hope you mean DMA errors, not really crashing.

Yes, I mean DMA errors. It just seems it crashed, because it never recovers
until reboot.

> What you describe here sounds like standard LP-PHY DMA issue resolved
> in 3.0 kernel. We got some timeouts-related bug, which didn't hit
> right after loading b43, usually some time (seconds-minutes) later.

Well, lately there wasn't always a timeout after loading b43. Sometimes, the DMA
error occured only after doing some more network intensive activity, like
downloading a file or watching a video on the web.

> The last patches are supposed to fix situation where DMA does not work
> at all. Not even for a second, not for a single packet. I'm really
> sure of that, unless you have some *really* bugged hardware accepting
> multiple "translation bits" (something my patches fix).
> Moreover LP-PHY DMA problems (timeouts issue) was known to be somehow
> CPU/BIOS-related. Which makes it even more probably that that's
> exactly what you were experiencing.

Honestly, I wouldn't know. I don't have quite fully understood what is that dma
translation bug causing the dma fatal errors.
However, I suspect it might be one of those *really* bugged hardware. I'm just
guessing, perhaps it has something to do with the DMA features enabled by the
Intel Virtualization Technology for Directed I/O. It's too much of a coincidence
that the DMA errors only happen when Intel VT is enabled.
Just for your reference, this is the system log extract regarding DMA on my
system.

kernel	[    0.257149] DMAR: Forcing write-buffer flush capability
kernel	[    0.257150] DMAR: Disabling IOMMU for graphics on this chipset
kernel	[    0.601514] PCI-DMA: Intel(R) Virtualization Technology for Directed
I/O
kernel	[    0.745975] ata1: SATA max UDMA/133 abar m2048@0xdf305000 port
0xdf305100 irq 49
kernel	[    0.745978] ata2: SATA max UDMA/133 abar m2048@0xdf305000 port
0xdf305180 irq 49
kernel	[    0.745983] ata5: SATA max UDMA/133 abar m2048@0xdf305000 port
0xdf305300 irq 49
kernel	[    0.745986] ata6: SATA max UDMA/133 abar m2048@0xdf305000 port
0xdf305380 irq 49
kernel	[    1.206589] ata1.00: ATA-8: FUJITSU MHZ2320BH G2, 8909, max UDMA/100
kernel	[    1.207251] ata1.00: configured for UDMA/100
kernel	[    1.682191] ata2.00: ATAPI: TSSTcorp CDDVDW TS-L633L, 0400, max
UDMA/100
kernel	[    1.695900] ata2.00: configured for UDMA/100
kernel	[    2.696557] mmc0: SDHCI controller on PCI [0000:06:00.1] using DMA
kernel	[   28.902798] DMAR:[DMA Read] Request device [02:00.0] fault addr
ffff4000 
kernel	[   28.902800] DMAR:[fault reason 06] PTE Read access is not set
kernel	[   28.902841] b43-phy0 ERROR: Fatal DMA error: 0x00000800, 0x00000000,
0x00000000, 0x00000000, 0x00000000, 0x00000000
kernel	[   28.902846] b43-phy0 ERROR: This device does not support DMA on your
system. It will now be switched to PIO.
kernel	[   28.902850] b43-phy0: Controller RESET (DMA error) ...

>From lspci, 02:00.0 refers to the Broadcom 4312 wireless card.

> That's the tricky part. Kernel 3.0 should really work for you. Unless
> Fedora got some problem (mistake?) in compiling/numbering...

> I think the important part was updating to the recent compat-wireless,
> not applying my patches. If you wish, you can still use that
> compat-wireless, revert my 2 patches and test again. I suspect card
> will be still working for you.

I booted back to the kernel 3.0 from fedora, without your patches and any
compat-wireless. I checked again and the DMA errors really continue in these
circunstances.
Then I booted again to my updated 3.0.3.rc1 kernel and I applied the same recent
compat-wireless without your last patches. Again, the same DMA errors occurred
after loading b43, as shown in the log above.
Only after patching the compat-wireless with your last patches and rebooting did
those DMA errors disappear. So I am afraid the recent (unpatched)
compat-wireless isn't the solution.


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