Re: [Xen-devel] [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 
---
  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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Re: [Xen-devel] [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,

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Julien Grall

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Re: [Xen-devel] [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 
>---
> 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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[Xen-devel] [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 
---
 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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