Re: [PATCH v2] MIPS64: Support of at least 48 bits of SEGBITS

[Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>]

On 05/15/2015 01:49 PM, David Daney wrote:
> On 05/14/2015 06:34 PM, Leonid Yegoshin wrote:
>> SEGBITS default is 40 bits or less, depending from CPU type.
>> This patch introduces 48bits of application virtual address (SEGBITS) 
>> support.
>> It is defined only for 16K and 64K pages and is optional (configurable).
>>
>> Penalty - a small number of additional pages for generic (small) 
>> applications.
>> But for 64K pages it adds 3rd level of PTE structure, which has a little
>> impact during software TLB refill.
>>
>> This patch is needed because MIPS I6XXX and P6XXX cores have 48 bit of
>> virtual address in each segment (SEGBITS).
>>
>
> Those processors don't require the patch.  You wrote the patch to give 
> a larger VA space at the request of kernel users.  So perhaps say:
>
>   The patch (optionally) increases the VA space available to userspace 
> processes from N-bits to 48-bits
>

... if CPU model supports that

>
>>
>> +config 48VMBITS
>
> Should probabaly be called VABITS instead of VMBITS to match the terms 
> used in the architecture reference manuals, as well as other ports 
> (ARM64).
>
> Perhaps MIPS_VA_BITS_48

I don't mind here. It can be even called 48SEGBITS or so, to match arch 
manual more. MIPS Arch manual never says about VA bits but speaks about 
PABITS and SEGBITS.

- Leonid.