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

[Hal Feng <hal.feng@starfivetech.com>]

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.

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.

> 
>> 
>> [1] https://www.sifive.com/cores/essential
>> 
>> > 
>> >> +			reg = <0>;
>> >> +			d-cache-block-size = <64>;
>> >> +			d-cache-sets = <64>;
>> >> +			d-cache-size = <8192>;
>> >> +			d-tlb-sets = <1>;
>> >> +			d-tlb-size = <40>;
>> >> +			device_type = "cpu";
>> >> +			i-cache-block-size = <64>;
>> >> +			i-cache-sets = <64>;
>> >> +			i-cache-size = <16384>;
>> >> +			i-tlb-sets = <1>;
>> >> +			i-tlb-size = <40>;
>> >> +			mmu-type = "riscv,sv39";
>> >> +			next-level-cache = <&ccache>;
>> >> +			riscv,isa = "rv64imac";
>> > 
>> > While I was poking around trying to see if there was some logic behind
>> > that compatible, I noticed that SiFive's docs for the S76 say it is
>> > RV64GBC *but* the docs for the u74-mc say "4xRV64GBC and 1xRV64IMAC".
>> > I assume that rv64imac is the correct one here?
>> 
>> 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.

> 
>> >> +			tlb-split;
>> >> +			status = "disabled";
>> >> +
>> >> +			cpu0_intc: interrupt-controller {
>> >> +				compatible = "riscv,cpu-intc";
>> >> +				interrupt-controller;
>> >> +				#interrupt-cells = <1>;
>> >> +			};
>> >> +		};
>> >> +
>> >> +		U74_1: cpu@1 {
>> >> +			compatible = "sifive,u74-mc", "riscv";
>> >> +			reg = <1>;
>> >> +			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 = "rv64imafdc";
>> > 
>> > That also begs the question:
>> > Do your u74s support RV64GBC, as the (current) SiFive documentation
>> > suggests?
>> 
>> Actually, U74 doesn't support the full B extension, and the SiFive doc [1]
> 
> Yeah, I knew asking that question that the "RV64GBC" in SiFive's online
> documentation was using outdated terminology. Also, that is not the doc
> for your core complex as far as I can tell. That is the document for
> impid 0x0621_1222, whereas (IIRC) your core is 0x0421_0427.
> Jess and I had a look one evening but could not find the 21G1.02.00
> revision of this document, which is the one corresponding to 0x421_0427.
> See Table 92 for more details.

I found the 21G1.02.00 revision on StarFive internal net, but I'm not sure
whether I can make it public and I am checking this. This revision records
that the ISA of 21G1.02.00 U74 is "RV64GCB" and ISA of 21G1.02.00 S7 is
"RV64IMACB". I am asking someone to check with SiFive whether both 21G1.02.00
U74 and S7 support the full B extension.

> 
>> describes the ISA of U74 is "RV64GC_Zba_Zbb_Sscofpmf" which "G" includes
>> "IMAFD".
> 
> I could not find the 21G1.02.00 version of this document online, but I
> was able to find the 21G1.01.00 version of it & that version does not
> support the Sscofpmf extension (but does have Zba/Zbb support).
> 
>> "_Zba_Zbb_Sscofpmf" is not shown in other device trees such as
>> jh7100.dtsi and fu740-c000.dtsi, so I didn't show them here.
> 
> Just because other devicetrees omit them, doesn't mean that you should
> too!
> This compatible should be an accurate description of your hardware, so
> you should add what you actually have.

Will keep it in mind. Thank you.

Best regards,
Hal

> If you have Zba and Zbb, then add them.
> I would double check against your internal documentation for 21G2.02.00
> as to whether you do have Sscofpmf, and if you do, add that too!
> 
> That way, whenever support for those extensions lands, the jh7110 will
> automatically pick it up, rather than needing to have them retrofitted.
> 
>> [1] https://sifive.cdn.prismic.io/sifive/2dd11994-693c-4360-8aea-5453d8642c42_u74mc_core_complex_manual_21G3.pdf