[Pixman] compatibility problem of Pixman on SOC system(such as ARMv7, or big.LITTLE)

Lennart Sorensen lsorense at csclub.uwaterloo.ca
Fri Jul 25 14:18:16 PDT 2014

On Thu, Jul 24, 2014 at 11:19:15AM +0000, Caoqiuhong wrote:
> Hello all pixman project members,
> From my email address, you can know that I am from silicon company Hisilicon in China, I am working with Android system on SOC platform.
> As we already known that Pixman embedded into Android system(android version is Kitkat, Pixman version is 0.30.0).
> I think Pixman already used by many applications in ARM soc system,
> Pixman used many optimization code according to different CPU architecture, such as X86, mips, arm. SIMD instruction set including SSE, NEON and so on.
> Now we just talk ARM CPU and NEON.
> A question from me is that have you tested Pixman on ARM big.LITTLE cpu?
> Now I found many games use pixel compositing feature Pixman supported, but the same pixel before compositing with the different output.
> The compositing output is correct on old ARM CPU(cores less than 4), incorrect on newest ARM CPU, such as 8-cores A7 CPU, and big.LITTLE(4 at A7, 4 at A15).
> Do you know this situation before? I found more games with this issue, compatible with qual-core ARM cpu, but pixel flaw with 8-core.

Which CPU model are you using?  Does it support using all 8 cores at once,
or does it switch between the A15 and A7 clusters?

If it uses all 8 cores at once, is the cache coherency correctly enabled
(The CCI)?  My understanding is that on many of the first designs this
wasn't the case.  If the cache coherency isn't working, that could almost
certainly cause issues with pixman.

I have a system on my desk with 8 cores but the kernel doesn't support
using the A7 cores yet (I should check if that has been fixed yet or not).

Len Sorensen

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