[OpenBIOS] [PATCH v3] ppc: SDR1 fixes

[Andreas Färber]

Am 21.11.2010 um 20:07 schrieb Alexander Graf:

> On 21.11.2010, at 18:50, Andreas Färber wrote:
>
>> Clean up use of SDR1 fields.
>>
>> IBM's "The Programming Environments for 32-Bit Microprocessors":
>> The HTABMASK field in SDR1 contains a mask value that determines
>> how many bits from the hash are used in the page table index. This  
>> mask
>> must be of the form 0b00...011...1; that is, a string of 0 bits  
>> followed by
>> a string of 1bits. The 1 bits determine how many additional bits  
>> (at least 10)
>> from the hash are used in the index; HTABORG must have this same  
>> number of
>> low-order bits equal to 0.
>>
>> IBM's "The Programming Environments Manual for 64-bit  
>> Microprocessors" 3.0:
>> The HTABSIZE field in SDR1 contains an integer value that determines
>> how many bits from the hash are used in the page table index. This  
>> number
>> must not exceed 28. HTABSIZE is used to generate a mask of the form
>> 0b00...011...1; that is, a string of 0 bits followed by a string of  
>> 1-bits.
>> The 1-bits determine how many additional bits (beyond the minimum  
>> of 11)
>> from the hash are used in the index. The HTABORG must have this  
>> same number
>> of low-order bits equal to 0.
>>
>> Adjust alignment mask and hash size for ppc64.
>>
>> Note that the page table does not yet scale with the memory size, and
>> the secondary hash is not yet used.
>>
>> v3:
>> * Fix shifts. Thanks to Segher and Alex.
>> * Fix HTABSIZE for 32-bit ppc64: ((2 << 15) - 1) >> 16 happened to  
>> be 0,
>> so that it worked as expected. Avoid underflow, spotted by Alex.
>> Make this fix available for legacy 64-bit support as well.
>> * Drop get_hash_size(). It was only used in hash_page_32() and caused
>> unnecessary conversions between HTABMASK and size.
>> * Introduce {mfsdr1,mtsdr1} as suggested by Alex.
>> Note that this changes the volatility for hash_page_64().
>> * Conditionalize 64-bit support, drop 32-bit support for ppc64.
>> * Adjust hash size for ppc64.
>>
>> v2:
>> * Use HTABSIZE for ppc64, fix HTABMASK usage for ppc.
>> Error spotted by Segher.
>>
>> Cc: Alexander Graf <agraf at suse.de>
>> Cc: Segher Boessenkool <segher at kernel.crashing.org>
>> Signed-off-by: Andreas Färber <andreas.faerber at web.de>

>> diff --git a/arch/ppc/qemu/ofmem.c b/arch/ppc/qemu/ofmem.c
>> index 72694b3..40a23ff 100644
>> --- a/arch/ppc/qemu/ofmem.c
>> +++ b/arch/ppc/qemu/ofmem.c

>> @@ -228,6 +223,11 @@ ea_to_phys( ucell ea, ucell *mode )
>> 	return phys;
>> }
>>
>> +#if defined(__powerpc64__) || defined(CONFIG_PPC_64BITSUPPORT)
>> +#ifndef CONFIG_PPC_64BITSUPPORT
>> +#define hash_page_64 hash_page
>> +#endif
>
> I'm not sure why, but this doesn't feel good :). Too much  
> preprocessor magic. Maybe explicitly call hash_page_64 or  
> hash_page_32 depending on the outcome of if_ppc64() and not  
> preprocess things?

Actually I am serious about getting rid of hash_page_32() in real  
ppc64 code. I have an idea to simplify this. On second thoughts the  
processor magic might be confusing when debugging.

Andreas