Subject: Re: [PATCH 09/11] powerpc/8xx: dont save CR in SCRATCH registers

From: leroy christophe <[email-masked]>
Date: Tue, 06 Jan 2015 08:07:27 +0100

Le 05/01/2015 19:30, Joakim Tjernlund a écrit :
> On Tue, 2014-12-16 at 16:03 +0100, Christophe Leroy wrote:
>> CR only needs to be preserved when checking if we are handling a kernel address.
>> So we can preserve CR in a register:
>> - In ITLBMiss, check is done only when CONFIG_MODULES is defined. Otherwise we
>> don't need to do anything at all with CR.
>> - If CONFIG_8xx_CPU6 is defined, we have r3 available for saving CR
>> - Otherwise, we use r10, then we reload SRR0/MD_EPN into r10 when CR is restored
> I think the #ifdef CPU6 code makes for too much maintenance. Can you
> loose the #ifdef CPU6 and adjust code so it works for both cases?
I wanted to take the opportunity to save one cycle, but we are wasting 
so many cycles with CPU6 that it is propably not worth it.
Ok, I will remove the special handling for CPU6.

>
>> Signed-off-by: Christophe Leroy <[email-masked]>
>>
>> ---
>>   arch/powerpc/kernel/head_8xx.S | 53 +++++++++++++++++++++++++++++-------------
>>   1 file changed, 37 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
>> index c89aed9..a073918 100644
>> --- a/arch/powerpc/kernel/head_8xx.S
>> +++ b/arch/powerpc/kernel/head_8xx.S
>> @@ -308,14 +308,10 @@ SystemCall:
>>   #endif
>>   
>>   InstructionTLBMiss:
>> +       EXCEPTION_PROLOG_0
>>   #ifdef CONFIG_8xx_CPU6
>>          mtspr   SPRN_DAR, r3
>>   #endif
>> -       EXCEPTION_PROLOG_0
>> -       mfcr    r10
>> -       mtspr   SPRN_SPRG_SCRATCH2, r10
>> -       mfspr   r10, SPRN_SRR0/* Get effective address of fault */
>> -       DO_8xx_CPU15(r11, r10)
>>   
>>          /* If we are faulting a kernel address, we have to use the
>>                  * kernel page tables.
>> @@ -323,14 +319,33 @@ InstructionTLBMiss:
>>   #ifdef CONFIG_MODULES
>>          /* Only modules will cause ITLB Misses as we always
>>                  * pin the first 8MB of kernel memory */
>> +#ifdef CONFIG_8xx_CPU6
>> +       mfspr   r10, SPRN_SRR0/* Get effective address of fault */
>> +       DO_8xx_CPU15(r11, r10)
>> +       mfcr    r3
>>          andis.  r11, r10, 0x8000/* Address >= 0x80000000 */
>> +#else
>> +       mfspr   r11, SPRN_SRR0/* Get effective address of fault */
>> +       DO_8xx_CPU15(r10, r11)
>> +       mfcr    r10
>> +       andis.  r11, r11, 0x8000/* Address >= 0x80000000 */
>>   #endif
>>          mfspr   r11, SPRN_M_TW/* Get level 1 table base address */
>> -#ifdef CONFIG_MODULES
>>          beq     3f
>>          lis     r11, (swapper_pg_dir-PAGE_OFFSET)@ha
>>   3:
>> +#ifdef CONFIG_8xx_CPU6
>> +       mtcr    r3
>> +#else
>> +       mtcr    r10
>> +       mfspr   r10, SPRN_SRR0/* Get effective address of fault */
>>   #endif
>> +#else /* CONFIG_MODULES */
>> +       mfspr   r10, SPRN_SRR0/* Get effective address of fault */
>> +       DO_8xx_CPU15(r11, r10)
>> +       mfspr   r11, SPRN_M_TW/* Get level 1 table base address */
>> +#endif /* CONFIG_MODULES */
>> +
>>          /* Insert level 1 index */
>>          rlwimi  r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
>>          lwz     r11, (swapper_pg_dir-PAGE_OFFSET)@l(r11)/* Get the level 1 entry */
>> @@ -362,29 +377,37 @@ InstructionTLBMiss:
>>          mfspr   r3, SPRN_DAR
>>          mtspr   SPRN_DAR, r11/* Tag DAR */
>>   #endif
>> -       mfspr   r10, SPRN_SPRG_SCRATCH2
>> -       mtcr    r10
>>          EXCEPTION_EPILOG_0
>>          rfi
>>   
>>          . = 0x1200
>>   DataStoreTLBMiss:
>> -#ifdef CONFIG_8xx_CPU6
>> -       mtspr   SPRN_DAR, r3
>> -#endif
>>          EXCEPTION_PROLOG_0
>> -       mfcr    r10
>> -       mtspr   SPRN_SPRG_SCRATCH2, r10
>> -       mfspr   r10, SPRN_MD_EPN
>>   
>>          /* If we are faulting a kernel address, we have to use the
>>                  * kernel page tables.
>>                  */
>> +#ifdef CONFIG_8xx_CPU6
>> +       mtspr   SPRN_DAR, r3
>> +       mfcr    r3
>> +       mfspr   r10, SPRN_MD_EPN
>>          andis.  r11, r10, 0x8000
>> +#else
>> +       mfcr    r10
>> +       mfspr   r11, SPRN_MD_EPN
>> +       andis.  r11, r11, 0x8000
>> +#endif
>>          mfspr   r11, SPRN_M_TW/* Get level 1 table base address */
>>          beq     3f
>>          lis     r11, (swapper_pg_dir-PAGE_OFFSET)@ha
>>   3:
>> +#ifdef CONFIG_8xx_CPU6
>> +       mtcr    r3
>> +#else
>> +       mtcr    r10
>> +       mfspr   r10, SPRN_MD_EPN
>> +#endif
>> +
>>          /* Insert level 1 index */
>>          rlwimi  r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
>>          lwz     r11, (swapper_pg_dir-PAGE_OFFSET)@l(r11)/* Get the level 1 entry */
>> @@ -441,8 +464,6 @@ DataStoreTLBMiss:
>>          mfspr   r3, SPRN_DAR
>>   #endif
>>          mtspr   SPRN_DAR, r11/* Tag DAR */
>> -       mfspr   r10, SPRN_SPRG_SCRATCH2
>> -       mtcr    r10
>>          EXCEPTION_EPILOG_0
>>          rfi
>>