Subject: Re[2]: [PATCH] powerpc 44x: support for 256KB PAGE_SIZE

From: Yuri Tikhonov <[email-masked]>
Date: Sun, 21 Dec 2008 14:36:42 +0300

Hello Milton,

 Thanks for reviewing. I'll re-post the updated patch shortly.

On Sunday, December 21, 2008 you wrote:

> On Dec 19, 2008, at 12:39 AM, Yuri Tikhonov wrote:

>> This patch adds support for 256KB pages on ppc44x-based boards.
>>

> Hi.  A couple of small comments.

>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index cd8ff7c..348702c 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -436,6 +436,14 @@ config PPC_64K_PAGES
>>       bool "64k page size" if 44x || PPC_STD_MMU_64
>>       select PPC_HAS_HASH_64K if PPC_STD_MMU_64
>>
>> +config PPC_256K_PAGES
>> +     bool "256k page size" if 44x
>> +     depends on !STDBINUTILS
>> +     help
>> +       ELF standard supports only page sizes up to 64K so you need a 
>> patched
>> +       binutils in order to use 256K pages. Chose it only if you know what
>> +       you are doing.
>> +

> Make the page size 256k.   As the ELF standard only requires alignment
> to
> support page sizes up to 64k, you will need to compile all of your user
> space applications with a patched binutils.

> Say N unless you know what you are doing.

> (The previous text did not describe what the option actually did, and 
> did not emphasize that all of user space had to be compiled).

>> diff --git a/arch/powerpc/include/asm/thread_info.h 
>> b/arch/powerpc/include/asm/thread_info.h
>> index 9665a26..3c8bbab 100644
>> --- a/arch/powerpc/include/asm/thread_info.h
>> +++ b/arch/powerpc/include/asm/thread_info.h
>> @@ -15,8 +15,12 @@
>>  #ifdef CONFIG_PPC64
>>  #define THREAD_SHIFT         14
>>  #else
>> +#ifdef CONFIG_PPC_256K_PAGES
>> +#define THREAD_SHIFT         15
>> +#else
>>  #define THREAD_SHIFT         13
>>  #endif
>> +#endif

> Switching to #elif would remove the nested ifdef here.

>>
>>  #define THREAD_SIZE          (1 << THREAD_SHIFT)
>>
>> diff --git a/arch/powerpc/kernel/head_booke.h 
>> b/arch/powerpc/kernel/head_booke.h
>> index fce2df9..bc6a26c 100644
>> --- a/arch/powerpc/kernel/head_booke.h
>> +++ b/arch/powerpc/kernel/head_booke.h
>> @@ -10,6 +10,14 @@
>>               mtspr   SPRN_IVOR##vector_number,r26;   \
>>               sync
>>
>> +#ifndef CONFIG_PPC_256K_PAGES

> This if should be on THREAD_SIZE or THREAD_SHIFT, not the option that 
> causes it to be large.

>> +#define ALLOC_STACK_FRAME(reg, val)  addi reg,reg,val
>> +#else
>> +#define ALLOC_STACK_FRAME(reg, val)                  \
>> +     addis   reg,reg,val@ha;                         \
>> +     addi    reg,reg,val@l
>> +#endif
>> +
>>  #define NORMAL_EXCEPTION_PROLOG                                                   \
>>       mtspr   SPRN_SPRG0,r10;         /* save two registers to work with */\
>>       mtspr   SPRN_SPRG1,r11;                                              \
>> @@ -20,7 +28,7 @@
>>       beq     1f;                                                          \
>>       mfspr   r1,SPRN_SPRG3;          /* if from user, start at top of   */\
>>       lwz     r1,THREAD_INFO-THREAD(r1); /* this thread's kernel stack   */\
>> -     addi    r1,r1,THREAD_SIZE;                                           \
>> +     ALLOC_STACK_FRAME(r1, THREAD_SIZE);                                  \
>>  1:   subi    r1,r1,INT_FRAME_SIZE;   /* Allocate an exception frame     */\
>>       mr      r11,r1;                                                      \
>>       stw     r10,_CCR(r11);          /* save various registers          */\
>> diff --git a/init/Kconfig b/init/Kconfig
>> index f763762..96229b9 100644
>> --- a/init/Kconfig
>> +++ b/init/Kconfig
>> @@ -635,6 +635,16 @@ config ELF_CORE
>>       help
>>         Enable support for generating core dumps. Disabling saves about 4k.
>>
>> +config STDBINUTILS
>> +     bool "Using standard binutils" if EMBEDDED
>> +     depends on 44x
>> +     default y
>> +     help
>> +       Turning this option off allows you to select 256KB PAGE_SIZE on 
>> 44x.
>> +       Note, that kernel will be able to run only those applications,
>> +       which had been compiled using the patched binutils (ELF standard
>> +       supports only page sizes up to 64K).
>> +

> The config variable 44x is pretty nondescript for a global config file.
>   If you leave it here, I would suggest  making it depend on PPC && 44x
> so that other people don't have to wonder what 44x means.  I didn't 
> look if there was a better place to put this option, somewhere 
> architecture specific might be better (eg after selecting the 44x cpu 
> type).

>>  config PCSPKR_PLATFORM
>>       bool "Enable PC-Speaker support" if EMBEDDED
>>       depends on ALPHA || X86 || MIPS || PPC_PREP || PPC_CHRP || 
>> PPC_PSERIES
>>

> thanks,
> milton

 Regards, Yuri

 --
 Yuri Tikhonov, Senior Software Engineer
 Emcraft Systems, www.emcraft.com