[PATCH 4/4] xen/arm: arm64: Remove MPIDR multiprocessing extensions check

[PATCH 4/4] xen/arm: arm64: Remove MPIDR multiprocessing extensions check

[Wei Chen]

In ARM64, the MPIDR multiprocessing extensions bit is reserved to 1.
So, the value check for this bit is no longer necessary on ARM64.

Signed-off-by: Wei Chen <Wei.Chen@linaro.org>
---
 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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Re: [PATCH 4/4] xen/arm: arm64: Remove MPIDR multiprocessing extensions check

[Peng Fan]

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@linaro.org>
>---
> 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
>
>
>_______________________________________________
>Xen-devel mailing list
>Xen-devel@lists.xen.org
>http://lists.xen.org/xen-devel

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

[Julien Grall]

Hello Peng,

On 25/05/16 13:37, Peng Fan wrote:
> 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?

Please read carefully the patch. The check on MPDIR_EL1.U is kept, only 
the check to the RES1 bit ('M' for Aarch32) is removed.

Regards,

-- 
Julien Grall

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

[Julien Grall]

Hi Wei,

On 25/05/16 03:10, Wei Chen wrote:
> In ARM64, the MPIDR multiprocessing extensions bit is reserved to 1.

Well, technically the bit is unamed for ARM64. So I would make clear 
that the name is from AArch32. Something along:

"The bit 31 (former bit Multiprocessing extensions bit in AArch32) is 
always RES1 for AArch64."

> So, the value check for this bit is no longer necessary on ARM64.
>
> Signed-off-by: Wei Chen <Wei.Chen@linaro.org>
> ---
>   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)
>

Regards,

-- 
Julien Grall

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