Re: [PATCH v3 6/7] riscv: dts: starfive: Add initial StarFive JH7110 device tree

[Conor Dooley <conor@kernel.org>]

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Hey Hal!

On Wed, Feb 15, 2023 at 11:07:15AM +0800, Hal Feng wrote:
> On Thu, 2 Feb 2023 19:41:33 +0000, Conor Dooley wrote:
> > On Fri, Feb 03, 2023 at 02:56:41AM +0800, Hal Feng wrote:
> >> On Wed, 1 Feb 2023 08:21:05 +0000, Conor Dooley wrote:
> >> > On Wed, Feb 01, 2023 at 03:21:48PM +0800, Hal Feng wrote:
> >> >> On Wed, 28 Dec 2022 22:48:43 +0000, Conor Dooley wrote:
> >> >> > On Tue, Dec 20, 2022 at 09:12:46AM +0800, Hal Feng wrote:
> >> > 
> >> >> >> +/ {
> >> >> >> +	compatible = "starfive,jh7110";
> >> >> >> +	#address-cells = <2>;
> >> >> >> +	#size-cells = <2>;
> >> >> >> +
> >> >> >> +	cpus {
> >> >> >> +		#address-cells = <1>;
> >> >> >> +		#size-cells = <0>;
> >> >> >> +
> >> >> >> +		S76_0: cpu@0 {
> >> >> >> +			compatible = "sifive,u74-mc", "riscv";
> >> >> > 
> >> >> > The label here says S76 but the compatible says u74-mc.
> >> >> 
> >> >> U74-MC has 5 cores including 1 * S7 core and 4 * U74 cores.
> >> >> 
> >> >> > Which is correct? Your docs say S7 and S76, so I would imagine that it
> >> >> > is actually an S76?
> >> >> 
> >> >> I found SiFive website [1] call it S76, but call it S7 in other places.
> >> >> So I misunderstood this. Considering the ISA difference you described
> >> >> as below, I think it's proper to change the label to "S7_0".
> >> > 
> >> > I'm less worried about the label & more interested in the compatible.
> >> > hart0 is, as you say, not a u74. Should we not be adding a "sifive,s7"
> >> > compatible string to Documentation/devicetree/bindings/riscv/cpus.yaml
> >> > and using that here instead?
> >> 
> >> First of all, it's my fault that I didn't check the revision of U74-MC
> >> manual, so most of my previous replies might not make sense.
> > 
> > No that's fine. The manual stuff confused me too when I went looking
> > initially, and I still get get mixed up by the fact that there are
> > core-complex manuals but not core manuals.
> > 
> >> If we add a new compatible string for S7, should we change the compatibles
> >> of hart1~3 to "sifive,u74" also? And then, there may be no point keeping some
> >> compatible strings of core complex like "sifive,u74-mc" and "sifive,u54-mc".
> >> I'm not sure about this.
> > 
> > [...]
> > 
> >> >> Yes, "RV64IMAC" is correct. The monitor core in U74-MC is a
> >> >> S7-series core, not S76.
> >> > 
> >> > Cool, thanks.
> >> 
> >> Now I think it might be another version of S76.
> > 
> > The SiFive docs describe the u74-mc core complex, which AFAIU you have,
> > as being 1x S7 & 4x U7.
> > 
> > I'd be happy with new binding for "sifive,s7" & then we use that here.
> > If you're sure it's S76, we can also use that. S76 is described, in what
> > docs I can see, as a core complex containing an S7, so S7 seems likely
> > to be correct?
> 
> I will add a new binding for "sifive,s7" and modify the code as follows.
> 
> 	S7_0: cpu@0 {
> 		compatible = "sifive,s7", "riscv";
> 		...
> 		riscv,isa = "rv64imac_zicsr_zba_zbb";

I'm not sure that I'd bother with the zicsr, it gets added automagically
by the Makefile if needed:
| # Newer binutils versions default to ISA spec version 20191213 which moves some
| # instructions from the I extension to the Zicsr and Zifencei extensions.
| toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
| riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei

Otherwise, thanks for the actual confirmation of zba/zbb!

Thanks,
Conor.


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