Re: [PATCH v2 03/24] target/mips/cpu: Introduce isa_rel6_available() helper

Philippe Mathieu-Daudé
2020-12-16T11:00:10Z

On 12/16/20 11:50 AM, Philippe Mathieu-Daudé wrote:
> On 12/16/20 4:14 AM, Jiaxun Yang wrote:
>> 在 2020/12/16 上午10:50, Jiaxun Yang 写道:
>>>
>>>
>>> TBH I do think it doesn't sounds like a good idea to make 32-bit
>>> and 64-bit different. In fact ISA_MIPS32R6 is always set for targets
>>> with ISA_MIPS64R6.
>>>
>>> We're treating MIPS64R6 as a superset of MIPS32R6, and ISA_MIPS3
>>> is used to tell if a CPU supports 64-bit.

I suppose you are talking about the CPU definitions
(CPU_MIPS32R6/CPU_MIPS64R6).

>
> Which is why I don't understand why they are 2 ISA_MIPS32R6/ISA_MIPS64R6
> definitions.

My comment is about the ISA definitions:

#define ISA_MIPS32 0x0000000000000020ULL
#define ISA_MIPS32R2 0x0000000000000040ULL
#define ISA_MIPS64 0x0000000000000080ULL
#define ISA_MIPS64R2 0x0000000000000100ULL
#define ISA_MIPS32R3 0x0000000000000200ULL
#define ISA_MIPS64R3 0x0000000000000400ULL
#define ISA_MIPS32R5 0x0000000000000800ULL
#define ISA_MIPS64R5 0x0000000000001000ULL
#define ISA_MIPS32R6 0x0000000000002000ULL
#define ISA_MIPS64R6 0x0000000000004000ULL

>
>>>
>>> FYI:
>>> https://commons.wikimedia.org/wiki/File:MIPS_instruction_set_family.svg
>>
>> Just add more cents here...
>> The current method we handle R6 makes me a little bit annoying.
>>
>> Given that MIPS is backward compatible until R5, and R6 reorganized a lot
>> of opcodes, I do think decoding procdure of R6 should be dedicated from
>> the rest,
>> otherwise we may fall into the hell of finding difference between R6 and
>> previous
>> ISAs, also I've heard some R6 only ASEs is occupying opcodes marked as
>> "removed in R6", so it doesn't looks like a wise idea to check removed
>> in R6
>> in helpers.
>
> I'm not sure I understood well your comment, but I also find how
> R6 is handled messy...
>
> I'm doing this removal (from helper to decoder) with the decodetree
> conversion.
>
>> So we may end up having four series of decodetrees for ISA
>> Series1: MIPS-II, MIPS32, MIPS32R2, MIPS32R5 (32bit "old" ISAs)
>> Series2: MIPS-III, MIPS64, MIPS64R2, MIPS64R5 (64bit "old" ISAs)
>>
>> Series3: MIPS32R6 (32bit "new" ISAs)
>> Series4: MIPS64R6 (64bit "new" ISAs)
>
> Something like that, I'm starting by converting the messier leaves
> first, so the R6 and ASEs. My approach is from your "series4" to
> "series1" last.
>
> Regards,
>
> Phil.
>