Re: [PATCH][v2] powerpc/mm: using two zones for freescale 64 bit kernel

On Aug 24, 2012, at 5:50 AM, Shaohui Xie wrote:

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.
=20
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.
=20
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.
=20
arch/powerpc/Kconfig      |    3 +++
arch/powerpc/kernel/dma.c |   15 +++++++++++++++
arch/powerpc/mm/mem.c     |    4 ++++
3 files changed, 22 insertions(+), 0 deletions(-)

Ben,

What's the feeling of doing this on ppc64 always?=20

- k

size_t size,

#else
	struct page *page;
	int node =3D dev_to_node(dev);
+#ifdef CONFIG_ZONE_DMA32
+	phys_addr_t top_ram_pfn =3D memblock_end_of_DRAM();
=20
+	/*
+	 * check for crappy device which has dma_mask < ZONE_DMA, and
+	 * we are not going to support it, just warn and fail.
+	 */
+	if (*dev->dma_mask < DMA_BIT_MASK(31)) {
+		dev_err(dev, "Unsupported dma_mask 0x%llx\n", =

*dev->dma_mask);