Re: [PATCH v2 14/17] riscv: dts: jh7110: Add initial StarFive JH7110 device tree

[yanhong wang <yanhong.wang@starfivetech.com>]

On 2023/1/20 2:30, Conor Dooley wrote:
> Hey Seán, David,
> 
> On Thu, Jan 19, 2023 at 01:26:52AM -0500, Sean Anderson wrote:
>> On 1/19/23 01:18, David Abdurachmanov wrote:
>> > On Wed, Jan 18, 2023 at 10:19 AM Yanhong Wang
>> > <yanhong.wang@starfivetech.com> wrote:
> 
>> > > +               U74_4: cpu@4 {
>> > > +                       compatible = "sifive,u74-mc", "riscv";
>> > > +                       reg = <4>;
>> > > +                       d-cache-block-size = <64>;
>> > > +                       d-cache-sets = <64>;
>> > > +                       d-cache-size = <32768>;
>> > > +                       d-tlb-sets = <1>;
>> > > +                       d-tlb-size = <40>;
>> > > +                       device_type = "cpu";
>> > > +                       i-cache-block-size = <64>;
>> > > +                       i-cache-sets = <64>;
>> > > +                       i-cache-size = <32768>;
>> > > +                       i-tlb-sets = <1>;
>> > > +                       i-tlb-size = <40>;
>> > > +                       mmu-type = "riscv,sv39";
>> > > +                       next-level-cache = <&ccache>;
>> > > +                       riscv,isa = "rv64imafdcbsu";
>> > 
>> > Looking at SiFive U74 manuals, shouldn't this be RV64GC_Zba_Zbb_Sscofpmf?
>> > U74 only supports Zba and Zbb bit manip extensions.
>> > This is from the 21G3.02.00 release manual.
>> > 
>> > Looking more, S76 core is listed in the manual as supporting up to:
>> > RV64IMAC_Zicsr_Zifencei_Zba_Zbb_Sscofpmf.
>> > 
>> > I almost forgot about _Zicsr_Zifencei (which are part of G). Shouldn't
>> > those be listed too in riscv,isa?
> 
> AFAIU, Linux just assumes them since they weren't their own thing prior
> to ISA spec 20191213. I think in- & ex- cluding them are both valid...
> Yeah.
> 
>> AFAIK we don't support Z/X in U-Boot.
> 
> Does the U-Boot ISA string parsing not just ignore un-implemented
> extensions? If it does ignore things you don't implement, then I think
> including the Z extensions should be no harm.
> IMO, it'd be nice to have this string match whatever the hardware can
> support so that same Devicetree can be used for U-Boot & whatever OS it
> is booting.
> 
> That said, I'm yet to be sure that this SoC supports Zba or Zbb.
> I asked on the corresponding patchset for Linux and the answer I got,
> not from the vendor, was that it did.
> To what extent it might (or if it actually does) I have not yet
> determined. It's not mentioned in any of the documentation that I have
> got my hands on.
> I have one of these boards, so am in the process of getting something
> functional enough on it to actually test that.
> 

Refer to the corresponding manual,the ISA definition of S7 is: rv64imac_zicsr_zba_zbb, 
and the ISA definition of U7 is: rv64imafdc_zicsr_zba_zbb, which is consistent with linux.

> Thanks!
> Conor.