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

[Conor Dooley <conor@kernel.org>]

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On Thu, Jan 19, 2023 at 02:16:51PM -0500, Sean Anderson wrote:
> On 1/19/23 13:30, 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.
> 
> We use strchr on it; so something like Zicsr is parsed as 5 extensions.

oof, that's rough :(

Just waiting until someone comes along that *needs* one of these
extensions to be functional?

> See supports_extension for details

Will do, thanks!
Conor.


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