Re: [Qemu-devel] [PATCH 2/7] target-mips: support Page Frame Number Extension field

[Leon Alrae <leon.alrae@imgtec.com>]

Hi James,

On 28/04/2015 14:35, James Hogan wrote:
> 
> 
> On 28/04/15 13:41, Leon Alrae wrote:
>> Update tlb->PFN to contain PFN concatenated with PFNX. PFNX is 0 if large
>> physical address is not supported.
>>
>> Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
>> ---
>>  target-mips/op_helper.c | 32 ++++++++++++++++++++++++++------
>>  1 file changed, 26 insertions(+), 6 deletions(-)
>>
>> diff --git a/target-mips/op_helper.c b/target-mips/op_helper.c
>> index c9a60bd..6bff927 100644
>> --- a/target-mips/op_helper.c
>> +++ b/target-mips/op_helper.c
>> @@ -1825,6 +1825,16 @@ static void r4k_mips_tlb_flush_extra (CPUMIPSState *env, int first)
>>      }
>>  }
>>  
>> +static inline uint64_t get_tlb_pfn_from_entrylo(uint64_t entrylo)
>> +{
>> +#if defined(TARGET_MIPS64)
>> +    return extract64(entrylo, 6, 54);
>> +#else
>> +    return extract64(entrylo, 6, 24) | /* PFN */
>> +           (extract64(entrylo, 32, 32) << 24); /* PFNX */
> 
> Where does the 32,32 come from? The PRA I have seems to imply that PFNX
> starts at bit 30 and goes up to bit 54.

This comes directly from MIPS32 PRA (I presume you are looking at MIPS64
PRA). Note that EntryLo.PFNX starts at bit 32 as there is 2-bit gap
occupied by RI/XI (unlike MIPS64 where it starts at bit 30).

Regards,
Leon