[PATCH v2 07/11] powerpc/8xx: macro for handling CPU15 errata

[PATCH v2 07/11] powerpc/8xx: macro for handling CPU15 errata

[Christophe Leroy]

Having a macro will help keep clear code.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

---
v2: no change

 arch/powerpc/kernel/head_8xx.S | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index a1571b3..065896f 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -297,6 +297,17 @@ SystemCall:
  * We have to use the MD_xxx registers for the tablewalk because the
  * equivalent MI_xxx registers only perform the attribute functions.
  */
+
+#ifdef CONFIG_8xx_CPU15
+#define DO_8xx_CPU15(tmp, addr)	\
+	addi	tmp, addr, PAGE_SIZE;	\
+	tlbie	tmp;			\
+	addi	tmp, addr, PAGE_SIZE;	\
+	tlbie	tmp
+#else
+#define DO_8xx_CPU15(tmp, addr)
+#endif
+
 InstructionTLBMiss:
 #ifdef CONFIG_8xx_CPU6
 	mtspr	SPRN_DAR, r3
@@ -304,12 +315,7 @@ InstructionTLBMiss:
 	EXCEPTION_PROLOG_0
 	mtspr	SPRN_SPRG_SCRATCH2, r10
 	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
-#ifdef CONFIG_8xx_CPU15
-	addi	r11, r10, PAGE_SIZE
-	tlbie	r11
-	addi	r11, r10, -PAGE_SIZE
-	tlbie	r11
-#endif
+	DO_8xx_CPU15(r11, r10)
 
 	/* If we are faulting a kernel address, we have to use the
 	 * kernel page tables.
-- 
2.1.0

RE: [PATCH v2 07/11] powerpc/8xx: macro for handling CPU15 errata

[David Laight]

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>From Christophe Leroy
> Having a macro will help keep clear code.

It might remove an #if but it doesn't really help.
All it means is that anyone reading the code has to hunt for
the definition before proceeding.

Some comment about what (and why) the extra code is needed
might help.

...
> +
> +#ifdef CONFIG_8xx_CPU15
> +#define DO_8xx_CPU15(tmp, addr)	\
> +	addi	tmp, addr, PAGE_SIZE;	\
> +	tlbie	tmp;			\
> +	addi	tmp, addr, PAGE_SIZE;	\

You've even transcribed this incorrectly.

Clearly not tested :-)

	David

> +	tlbie	tmp
> +#else
> +#define DO_8xx_CPU15(tmp, addr)
> +#endif
> +
>  InstructionTLBMiss:
>  #ifdef CONFIG_8xx_CPU6
>  	mtspr	SPRN_DAR, r3
> @@ -304,12 +315,7 @@ InstructionTLBMiss:
>  	EXCEPTION_PROLOG_0
>  	mtspr	SPRN_SPRG_SCRATCH2, r10
>  	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
> -#ifdef CONFIG_8xx_CPU15
> -	addi	r11, r10, PAGE_SIZE
> -	tlbie	r11
> -	addi	r11, r10, -PAGE_SIZE
> -	tlbie	r11
> -#endif
> +	DO_8xx_CPU15(r11, r10)
> 
>  	/* If we are faulting a kernel address, we have to use the
>  	 * kernel page tables.
> --
> 2.1.0
> 
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev
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Re: [PATCH v2 07/11] powerpc/8xx: macro for handling CPU15 errata

[leroy christophe]

Le 20/01/2015 12:09, David Laight a écrit :
>  From Christophe Leroy
>> Having a macro will help keep clear code.
> It might remove an #if but it doesn't really help.
> All it means is that anyone reading the code has to hunt for
> the definition before proceeding.
>
> Some comment about what (and why) the extra code is needed
> might help.
The main reason is because of patch 09/11 where we have to duplicate 
this code. I prefer to just duplicate one line rather than duplicate the 
whole code (especially because in v1 of the PATCHset, it was duplicated 
twice):

-    DO_8xx_CPU15(r11, r10)
[...]
#ifdef CONFIG_MODULES
[...]
+    DO_8xx_CPU15(r10, r11)
[...]
+#else
+    mfspr    r10, SPRN_SRR0    /* Get effective address of fault */
+    DO_8xx_CPU15(r11, r10)

Is this approach wrong ?


>
> ...
>> +
>> +#ifdef CONFIG_8xx_CPU15
>> +#define DO_8xx_CPU15(tmp, addr)	\
>> +	addi	tmp, addr, PAGE_SIZE;	\
>> +	tlbie	tmp;			\
>> +	addi	tmp, addr, PAGE_SIZE;	\
> You've even transcribed this incorrectly.
Oops
>
> Clearly not tested :-)
Indeed it's been tested, but tests can only show that the code is not 
worth than before.
This code is there to fix a chip errata which (almost?) never happens.
In my production version, I have not activated this errata, and he have 
never seen the problem on any of the more than 200 boards that have run 
for at least 4 years.

Christophe
>
> 	David
>
>> +	tlbie	tmp
>> +#else
>> +#define DO_8xx_CPU15(tmp, addr)
>> +#endif
>> +
>>   InstructionTLBMiss:
>>   #ifdef CONFIG_8xx_CPU6
>>   	mtspr	SPRN_DAR, r3
>> @@ -304,12 +315,7 @@ InstructionTLBMiss:
>>   	EXCEPTION_PROLOG_0
>>   	mtspr	SPRN_SPRG_SCRATCH2, r10
>>   	mfspr	r10, SPRN_SRR0	/* Get effective address of fault */
>> -#ifdef CONFIG_8xx_CPU15
>> -	addi	r11, r10, PAGE_SIZE
>> -	tlbie	r11
>> -	addi	r11, r10, -PAGE_SIZE
>> -	tlbie	r11
>> -#endif
>> +	DO_8xx_CPU15(r11, r10)
>>
>>   	/* If we are faulting a kernel address, we have to use the
>>   	 * kernel page tables.
>> --
>> 2.1.0
>>
>> _______________________________________________
>> Linuxppc-dev mailing list
>> Linuxppc-dev@lists.ozlabs.org
>> https://lists.ozlabs.org/listinfo/linuxppc-dev

RE: [PATCH v2 07/11] powerpc/8xx: macro for handling CPU15 errata

[David Laight]

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From: leroy 
> Le 20/01/2015 12:09, David Laight a écrit :
> >  From Christophe Leroy
> >> Having a macro will help keep clear code.
> > It might remove an #if but it doesn't really help.
> > All it means is that anyone reading the code has to hunt for
> > the definition before proceeding.
> >
> > Some comment about what (and why) the extra code is needed
> > might help.
> The main reason is because of patch 09/11 where we have to duplicate
> this code. I prefer to just duplicate one line rather than duplicate the
> whole code (especially because in v1 of the PATCHset, it was duplicated
> twice):
> 
> -    DO_8xx_CPU15(r11, r10)
> [...]
> #ifdef CONFIG_MODULES
> [...]
> +    DO_8xx_CPU15(r10, r11)
> [...]
> +#else
> +    mfspr    r10, SPRN_SRR0    /* Get effective address of fault */
> +    DO_8xx_CPU15(r11, r10)
> 
> Is this approach wrong ?

I'd call it something that infers 'invalidate adjacent pages'
and then mention that this is needed due to a cpu errata.

	David

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