Re: [Xen-devel] [PATCH 4/4] xen/arm: arm64: Remove MPIDR multiprocessing extensions check

[Peng Fan <van.freenix@xxxxxxxxx>]

Hi Wei,

On Wed, May 25, 2016 at 10:10:11AM +0800, Wei Chen wrote:
>In ARM64, the MPIDR multiprocessing extensions bit is reserved to 1.
>So, the value check for this bit is no longer necessary on ARM64.

From ARM DDI0487A.G, I found the U bit for MPIDR_EL1:
"
Indicates a Uniprocessor system, as distinct from PE 0 in a multiprocessor 
system. The possible
values of this bit are:
0 Processor is part of a multiprocessor system.
1 Processor is part of a uniprocessor system.
"

It's not reserved to 1. Which doc are you refering to?

Regards,
Peng.

>
>Signed-off-by: Wei Chen <Wei.Chen@xxxxxxxxxx>
>---
> xen/arch/arm/arm64/head.S | 1 -
> 1 file changed, 1 deletion(-)
>
>diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
>index 3090beb..91e2817 100644
>--- a/xen/arch/arm/arm64/head.S
>+++ b/xen/arch/arm/arm64/head.S
>@@ -267,7 +267,6 @@ common_start:
>                                       * find that multiprocessor extensions 
> are
>                                       * present and the system is SMP  */
>         mrs   x0, mpidr_el1
>-        tbz   x0, _MPIDR_SMP, 1f     /* Multiprocessor extension not 
>supported? */
>         tbnz  x0, _MPIDR_UP, 1f      /* Uniprocessor system? */
> 
>         ldr   x13, =(~MPIDR_HWID_MASK)
>-- 
>2.7.4
>
>
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