On Thu, 2012-08-30 at 15:49 -0500, Kumar Gala wrote:
On Aug 24, 2012, at 5:50 AM, Shaohui Xie wrote:
quoted
PowerPC platform only supports ZONE_DMA zone for 64bit kernel, so all the
memory will be put into this zone. If the memory size is greater than
the device's DMA capability and device uses dma_alloc_coherent to allocate
memory, it will get an address which is over the device's DMA addressing,
the device will fail.
So we split the memory to two zones: zone ZONE_DMA32 & ZONE_NORMAL, since
we already allocate PCICSRBAR/PEXCSRBAR right below the 4G boundary (if the
lowest PCI address is above 4G), so we constrain the DMA zone ZONE_DMA32
to 2GB, also, we clear flag __GFP_DMA & __GFP_DMA32 and set __GFP_DMA32 only
if the device's dma_mask < total memory size. By doing this, devices which
cannot DMA all the memory will be limited to ZONE_DMA32, but devices which
can DMA all the memory will not be affected by this limitation.
Signed-off-by: Shaohui Xie <redacted>
Signed-off-by: Mingkai Hu <redacted>
Signed-off-by: Chen Yuanquan <redacted>
---
changes for v2:
1. use a config option for using two zones (ZONE_DMA32 & ZONE_NORMAL) in
freescale 64 bit kernel.
There must have been a misunderstanding. I think this should be a
runtime choice, possibly by the platform code. Any reason that can't be
done ?
Also how does Intel do it ? Do they have iommu and ZONE_DMA32 co-exist ?
Cheers,
Ben.