[PATCH 1/2] arm: mvebu: increase atomic coherent pool size for armada 370/XP

On Thursday 25 October 2012, Thomas Petazzoni wrote:

On Thu, 25 Oct 2012 11:27:36 +0000, Arnd Bergmann wrote:

quoted

On Wednesday 24 October 2012, Gregory CLEMENT wrote:

quoted

For Armada 370/XP we have the same problem that for the commit
cb01b63, so we applied the same solution: "The default 256 KiB
coherent pool may be too small for some of the Kirkwood devices, so
increase it to make sure that devices will be able to allocate their
buffers with GFP_ATOMIC flag"

Signed-off-by: Gregory CLEMENT <redacted>

Do you know why the ATA driver needs this? I find it surprising that
it's necessary, so I'd like to make sure we're not just working around
a device driver bug here.

The sata_mv driver create dma_pool and allocate objects from them, and
all the memory allocated for dma_pools is allocated using
dma_alloc_coherent(), and I guess the driver is using too much of them.

Seems like the driver is too lazy and allocates everything coherent to
avoid the hassle of doing dma_map/dma_unmap operations when needed, but
I haven't looked in details at the driver yet to see if it would be
possible to switch those DMA coherent allocations into non-coherent
allocations + appropriate calls to the DMA operations.

Using coherent allocations is fine, I was wondering whether they need
to be atomic or not.

That said, that's for sure a larger task than just enabling SATA on
Armada 370/XP, so I would advocate to handle this problem separately.

Agreed.

	Arnd