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

Philippe Mathieu-Daudé
2021-01-07T13:18:56Z

On 1/7/21 10:04 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.
>>>
>>> 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 think we are in agreement :) Your comment seems what I addressed
> last month as this series:
> https://gitlab.com/philmd/qemu/-/commits/mips_decodetree_lsa_r6/
> (I'll try to rebase it and post during the week-end.)

Bah actually it is already on the list and reviewed =)
https://www.mail-archive.com/qemu-devel@nongnu.org/msg765234.html

>> 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)
>>
>> Thanks
>>
>> - Jiaxun
>