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

[Thomas Petazzoni]

Arnd,

On Thu, 25 Oct 2012 11:27:36 +0000, Arnd Bergmann wrote:
> On Wednesday 24 October 2012, Gregory CLEMENT wrote:
> > 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 <gregory.clement@xxxxxxxxxxxxxxxxxx>
> 
> 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.

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.

Best regards,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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