Replacing dma_alloc_writecombine for aarch64

Replacing dma_alloc_writecombine for aarch64

[Ryan Harkin]

Hi Catalin,

Some time ago, I converted the PL111 driver to use device tree [1].  I
gathered some feedback after an RFC and I was recently updating my
driver.  However, with my aarch64 work, I found that the driver
doesn't compile for aarch64 because I've been using
dma_alloc_writecombine in the driver.  As aarch64 doesn't use the
driver with DMA, I hacked it to get my aarch64 branch working.

Is there another API you can recommend I use for DMA that will work
with both flavours?

Regards,
Ryan.

[1] http://git.linaro.org/gitweb?p=landing-teams/working/arm/kernel.git;a=shortlog;h=refs/heads/tracking-armlt-clcd

Replacing dma_alloc_writecombine for aarch64

[Catalin Marinas]

On Mon, Dec 03, 2012 at 05:18:35PM +0000, Ryan Harkin wrote:
> Some time ago, I converted the PL111 driver to use device tree [1].  I
> gathered some feedback after an RFC and I was recently updating my
> driver.  However, with my aarch64 work, I found that the driver
> doesn't compile for aarch64 because I've been using
> dma_alloc_writecombine in the driver.  As aarch64 doesn't use the
> driver with DMA, I hacked it to get my aarch64 branch working.
> 
> Is there another API you can recommend I use for DMA that will work
> with both flavours?

You can use dma_alloc_coherent() which gives the same thing on ARMv7
(and some ARMv6) and AArch64 (write-combine memory). However, there is
ARMv5 where this translates to strongly ordered memory, so you can't the
coherent variant all the time.

-- 
Catalin

Replacing dma_alloc_writecombine for aarch64

[Ryan Harkin]

On 3 December 2012 17:25, Catalin Marinas <catalin.marinas@arm.com> wrote:
> On Mon, Dec 03, 2012 at 05:18:35PM +0000, Ryan Harkin wrote:
>> Some time ago, I converted the PL111 driver to use device tree [1].  I
>> gathered some feedback after an RFC and I was recently updating my
>> driver.  However, with my aarch64 work, I found that the driver
>> doesn't compile for aarch64 because I've been using
>> dma_alloc_writecombine in the driver.  As aarch64 doesn't use the
>> driver with DMA, I hacked it to get my aarch64 branch working.
>>
>> Is there another API you can recommend I use for DMA that will work
>> with both flavours?
>
> You can use dma_alloc_coherent() which gives the same thing on ARMv7
> (and some ARMv6) and AArch64 (write-combine memory). However, there is
> ARMv5 where this translates to strongly ordered memory, so you can't the
> coherent variant all the time.

Thanks, Catalin.  I'll give it a go.

I'm slightly worried about the ARMv5 comment as I probably have to
take into account that my driver may get used there, but I'll see how
it shakes out on vexpress first.

Cheers,
Ryan.