PPC64 & DMA zone

Hi,

Is there a way to reduce/limit DMA zone with PPC64 kernel (3.6-rcX)
on G5 Mac? I have tried to search Kconfig or command line options,
but can't find anything.

The problem I have is that b43 driver (wireless chip) insists a 30-bit
DMA mask, but I have 1.5 GB physical memory. So the only way I can get
the wireless connection to work is to boot with "mem=1024MB". And as a
result my bloaty applications will loose much needed memory...

Thanks,

A.

On Fri, 2012-08-17 at 23:04 +0300, Aaro Koskinen wrote:

Hi,

Is there a way to reduce/limit DMA zone with PPC64 kernel (3.6-rcX)
on G5 Mac? I have tried to search Kconfig or command line options,
but can't find anything.

No.

The problem I have is that b43 driver (wireless chip) insists a 30-bit
DMA mask, but I have 1.5 GB physical memory. So the only way I can get
the wireless connection to work is to boot with "mem=1024MB". And as a
result my bloaty applications will loose much needed memory...

Or force the iommu to be enabled, it should be able to service
constrained DMA (iommu=force on the command line).

Cheers,
Ben.

Hi,

On Sat, Aug 18, 2012 at 06:40:56AM +1000, Benjamin Herrenschmidt wrote:

quoted

The problem I have is that b43 driver (wireless chip) insists a 30-bit
DMA mask, but I have 1.5 GB physical memory. So the only way I can get
the wireless connection to work is to boot with "mem=1024MB". And as a
result my bloaty applications will loose much needed memory...

Or force the iommu to be enabled, it should be able to service
constrained DMA (iommu=force on the command line).

I still get the same failure:

DART IOMMU initialized for U3 type chipset
[...]
Kernel command line: ramdisk_size=8192 iommu=force
[...]
Top of RAM: 0x60000000, Total RAM: 0x60000000
Memory hole size: 0MB
Zone ranges:
  DMA      [mem 0x00000000-0x5fffffff]
  Normal   empty
[...]
b43-pci-bridge 0001:01:01.0: Warning: IOMMU window too big for device mask
b43-pci-bridge 0001:01:01.0: mask: 0x3fffffff, table end: 0x80000000
b43-phy0 ERROR: The machine/kernel does not support the required 30-bit DMA mask

A.

On Sat, 2012-08-18 at 00:01 +0300, Aaro Koskinen wrote:

b43-pci-bridge 0001:01:01.0: Warning: IOMMU window too big for device
mask
b43-pci-bridge 0001:01:01.0: mask: 0x3fffffff, table end: 0x80000000
b43-phy0 ERROR: The machine/kernel does not support the required
30-bit DMA mask

Hrm, odd, I though we had the iommu allocator sorted to handle that case
a while back. Maybe that got broken. I can try to have a look but poke
me in a week or so if you don't hear from me.

Unless somebody else beat me to it which would be much welcome :-)

Cheers,
Ben.

On Fri, Aug 17, 2012 at 3:40 PM, Benjamin Herrenschmidt
[off-list ref] wrote:

On Fri, 2012-08-17 at 23:04 +0300, Aaro Koskinen wrote:

quoted

Hi,

Is there a way to reduce/limit DMA zone with PPC64 kernel (3.6-rcX)
on G5 Mac? I have tried to search Kconfig or command line options,
but can't find anything.

No.

What about Shaohui patches for ZONE_DMA?  That's meant to solve
exactly this problem?  Granted, it sets the DMA zone to 31 bits, but
it's simple to hack that to 30 bits.

--=20
Timur Tabi
Linux kernel developer at Freescale=

On Sun, 2012-09-02 at 02:54 +0000, Tabi Timur-B04825 wrote:

On Fri, Aug 17, 2012 at 3:40 PM, Benjamin Herrenschmidt
[off-list ref] wrote:

quoted

On Fri, 2012-08-17 at 23:04 +0300, Aaro Koskinen wrote:

quoted

Hi,

Is there a way to reduce/limit DMA zone with PPC64 kernel (3.6-rcX)
on G5 Mac? I have tried to search Kconfig or command line options,
but can't find anything.

No.

What about Shaohui patches for ZONE_DMA?  That's meant to solve
exactly this problem?  Granted, it sets the DMA zone to 31 bits, but
it's simple to hack that to 30 bits.

Unnecessary for this specific problem. The right fix to the iommu code
has already been done.

Cheers,
Ben.