On 07/18/2013 12:32:18 PM, Alexander Graf wrote:
On 18.07.2013, at 19:17, Scott Wood wrote:
> On 07/18/2013 08:19:03 AM, Bharat Bhushan wrote:
> Likewise, we want to make sure this matches the host entry.
Unfortunately, this is a bit of a mess already. 64-bit booke appears
to always set MAS2_M for TLB0 mappings. The initial KERNELBASE
mapping on boot uses M_IF_SMP, and the settlbcam() that (IIRC)
replaces it uses _PAGE_COHERENT. 32-bit always uses _PAGE_COHERENT,
except that initial KERNELBASE mapping. _PAGE_COHERENT appears to be
set based on CONFIG_SMP || CONFIG_PPC_STD_MMU (the latter config
clears _PAGE_COHERENT in the non-CPU_FTR_NEED_COHERENT case).
>
> As for what we actually want to happen, there are cases when we
want M to be set for non-SMP. One such case is AMP, where CPUs may
be sharing memory even if the Linux instance only runs on one CPU
(this is not hypothetical, BTW). It's also possible that we
encounter a hardware bug that requires MAS2_M, similar to what some
of our non-booke chips require.
How about we always set M then for RAM?
M is like I in that bad things happen if you mix them. So we really
want to match exactly what the rest of the kernel is doing.
Plus, the performance penalty on some single-core chips can be pretty
bad.
-Scott
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