Re: [Xen-devel] [PATCH 2/2] xen/arm64: use shift operator

2016-04-23 Thread Peng Fan 
Hi Julien,
On Fri, Apr 22, 2016 at 05:08:26PM +0100, Julien Grall wrote:
>On 21/04/16 02:06, Peng Fan wrote:
>>Hi Julien,
>
>Hello Peng,
>
>>On Wed, Apr 20, 2016 at 03:44:09PM +0100, Julien Grall wrote:
>>>Hello Peng,
>>>
>>>On 20/04/16 14:54, Peng Fan wrote:
Use shift operator, but not muliplication.
No function change.
>>>
>>>Why? The compiler will calculate the address at compilation time.
>>
>>Yeah. The compiler will do this. I just think in asm, we rarely use
>>multiplication. In this file, there is "cmp   x1, #(LPAE_ENTRIES<<3)",
>>here use shift operator but not multiplication.
>
>It took me a bit of time to understand that 8 is the number of byte of an
>LPAE entries. IMHO the "<< 3" would be more confusing.
>
>So I would introduce a macro to get the slot based of an index. Something
>like:
>
>LPAE_SLOT(slot) ((slot) * 8)
>
>And add a comment to explain why 8. You could even introduce LPAE_ENTRY_SIZE.

Thanks for comments. I'll try to submit a new patch following your suggestion.

Thanks,
Peng.

>
>Regards,
>
>>Thanks,
>>Peng.
>>
>>>
>>>Regards,
>>>
Signed-off-by: Peng Fan 
Cc: Stefano Stabellini 
Cc: Julien Grall 
---
  xen/arch/arm/arm64/head.S | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 05e3db0..ad6e593 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -524,7 +524,7 @@ paging:
  lsl   x2, x2, #THIRD_SHIFT   /* 4K aligned paddr of UART */
  mov   x3, #PT_DEV_L3
  orr   x2, x2, x3 /* x2 := 4K dev map including UART */
-str   x2, [x1, #(FIXMAP_CONSOLE*8)] /* Map it in the first 
fixmap's slot */
+str   x2, [x1, #(FIXMAP_CONSOLE << 3)] /* Map it in the first 
fixmap's slot */
  1:

  /* Map fixmap into boot_second */

>>>
>>>--
>>>Julien Grall
>>
>
>-- 
>Julien Grall

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Re: [Xen-devel] [PATCH 2/2] xen/arm64: use shift operator

2016-04-22 Thread Julien Grall 

On 21/04/16 02:06, Peng Fan wrote:

Hi Julien,


Hello Peng,


On Wed, Apr 20, 2016 at 03:44:09PM +0100, Julien Grall wrote:

Hello Peng,

On 20/04/16 14:54, Peng Fan wrote:

Use shift operator, but not muliplication.
No function change.


Why? The compiler will calculate the address at compilation time.


Yeah. The compiler will do this. I just think in asm, we rarely use
multiplication. In this file, there is "cmp   x1, #(LPAE_ENTRIES<<3)",
here use shift operator but not multiplication.


It took me a bit of time to understand that 8 is the number of byte of 
an LPAE entries. IMHO the "<< 3" would be more confusing.


So I would introduce a macro to get the slot based of an index. 
Something like:


LPAE_SLOT(slot) ((slot) * 8)

And add a comment to explain why 8. You could even introduce 
LPAE_ENTRY_SIZE.


Regards,


Thanks,
Peng.



Regards,


Signed-off-by: Peng Fan 
Cc: Stefano Stabellini 
Cc: Julien Grall 
---
  xen/arch/arm/arm64/head.S | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 05e3db0..ad6e593 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -524,7 +524,7 @@ paging:
  lsl   x2, x2, #THIRD_SHIFT   /* 4K aligned paddr of UART */
  mov   x3, #PT_DEV_L3
  orr   x2, x2, x3 /* x2 := 4K dev map including UART */
-str   x2, [x1, #(FIXMAP_CONSOLE*8)] /* Map it in the first fixmap's 
slot */
+str   x2, [x1, #(FIXMAP_CONSOLE << 3)] /* Map it in the first fixmap's 
slot */
  1:

  /* Map fixmap into boot_second */



--
Julien Grall




--
Julien Grall

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Re: [Xen-devel] [PATCH 2/2] xen/arm64: use shift operator

2016-04-20 Thread Peng Fan 
Hi Julien,

On Wed, Apr 20, 2016 at 03:44:09PM +0100, Julien Grall wrote:
>Hello Peng,
>
>On 20/04/16 14:54, Peng Fan wrote:
>>Use shift operator, but not muliplication.
>>No function change.
>
>Why? The compiler will calculate the address at compilation time.

Yeah. The compiler will do this. I just think in asm, we rarely use
multiplication. In this file, there is "cmp   x1, #(LPAE_ENTRIES<<3)",
here use shift operator but not multiplication.

Thanks,
Peng.

>
>Regards,
>
>>Signed-off-by: Peng Fan 
>>Cc: Stefano Stabellini 
>>Cc: Julien Grall 
>>---
>>  xen/arch/arm/arm64/head.S | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>>diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
>>index 05e3db0..ad6e593 100644
>>--- a/xen/arch/arm/arm64/head.S
>>+++ b/xen/arch/arm/arm64/head.S
>>@@ -524,7 +524,7 @@ paging:
>>  lsl   x2, x2, #THIRD_SHIFT   /* 4K aligned paddr of UART */
>>  mov   x3, #PT_DEV_L3
>>  orr   x2, x2, x3 /* x2 := 4K dev map including UART */
>>-str   x2, [x1, #(FIXMAP_CONSOLE*8)] /* Map it in the first fixmap's 
>>slot */
>>+str   x2, [x1, #(FIXMAP_CONSOLE << 3)] /* Map it in the first 
>>fixmap's slot */
>>  1:
>>
>>  /* Map fixmap into boot_second */
>>
>
>-- 
>Julien Grall

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Re: [Xen-devel] [PATCH 2/2] xen/arm64: use shift operator

2016-04-20 Thread Julien Grall 

Hello Peng,

On 20/04/16 14:54, Peng Fan wrote:

Use shift operator, but not muliplication.
No function change.


Why? The compiler will calculate the address at compilation time.

Regards,


Signed-off-by: Peng Fan 
Cc: Stefano Stabellini 
Cc: Julien Grall 
---
  xen/arch/arm/arm64/head.S | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 05e3db0..ad6e593 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -524,7 +524,7 @@ paging:
  lsl   x2, x2, #THIRD_SHIFT   /* 4K aligned paddr of UART */
  mov   x3, #PT_DEV_L3
  orr   x2, x2, x3 /* x2 := 4K dev map including UART */
-str   x2, [x1, #(FIXMAP_CONSOLE*8)] /* Map it in the first fixmap's 
slot */
+str   x2, [x1, #(FIXMAP_CONSOLE << 3)] /* Map it in the first fixmap's 
slot */
  1:

  /* Map fixmap into boot_second */



--
Julien Grall

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[Xen-devel] [PATCH 2/2] xen/arm64: use shift operator

2016-04-20 Thread Peng Fan 
Use shift operator, but not muliplication.
No function change.

Signed-off-by: Peng Fan 
Cc: Stefano Stabellini 
Cc: Julien Grall 
---
 xen/arch/arm/arm64/head.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 05e3db0..ad6e593 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -524,7 +524,7 @@ paging:
 lsl   x2, x2, #THIRD_SHIFT   /* 4K aligned paddr of UART */
 mov   x3, #PT_DEV_L3
 orr   x2, x2, x3 /* x2 := 4K dev map including UART */
-str   x2, [x1, #(FIXMAP_CONSOLE*8)] /* Map it in the first fixmap's 
slot */
+str   x2, [x1, #(FIXMAP_CONSOLE << 3)] /* Map it in the first fixmap's 
slot */
 1:
 
 /* Map fixmap into boot_second */
-- 
2.6.2


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