linux-kernel - Re: [PATCH v1 2/2] riscv: dts: starfive: add the missing monitor core

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Message-ID: <1dc0f29b40d34bc6472ba4139ff36f63e9cc9e84.camel@icenowy.me>
Date:   Wed, 13 Jul 2022 23:12:37 +0800
From:   Icenowy Zheng <uwu@...nowy.me>
To:     Conor.Dooley@...rochip.com, kernel@...il.dk, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, paul.walmsley@...ive.com,
        palmer@...belt.com, aou@...s.berkeley.edu, anup@...infault.org
Cc:     devicetree@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] riscv: dts: starfive: add the missing monitor
 core

在 2022-07-13星期三的 15:09 +0000，Conor.Dooley@...rochip.com写道：
> 
> 
> On 13/07/2022 16:02, Icenowy Zheng wrote:
> > 在 2022-07-13星期三的 14:55 +0000，Conor.Dooley@...rochip.com写道：
> > > On 13/07/2022 15:26, Icenowy Zheng wrote:
> > > > 
> > > > 在 2022-07-11星期一的 19:43 +0100，Conor Dooley写道：
> > > > > From: Conor Dooley <conor.dooley@...rochip.com>
> > > > > 
> > > > > The JH7100 has a 32 bit monitor core that is missing from the
> > > > > device
> > > > > tree. Add it (and its cpu-map entry) to more accurately
> > > > > reflect
> > > > > the
> > > > > actual topology of the SoC.
> > > > > 
> > > > > Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> > > > > ---
> > > > >  arch/riscv/boot/dts/starfive/jh7100.dtsi | 21
> > > > > +++++++++++++++++++++
> > > > >  1 file changed, 21 insertions(+)
> > > > > 
> > > > > diff --git a/arch/riscv/boot/dts/starfive/jh7100.dtsi
> > > > > b/arch/riscv/boot/dts/starfive/jh7100.dtsi
> > > > > index c617a61e26e2..92fce5b66d3d 100644
> > > > > --- a/arch/riscv/boot/dts/starfive/jh7100.dtsi
> > > > > +++ b/arch/riscv/boot/dts/starfive/jh7100.dtsi
> > > > > @@ -67,6 +67,23 @@ cpu1_intc: interrupt-controller {
> > > > >                         };
> > > > >                 };
> > > > > 
> > > > > +               E24: cpu@2 {
> > > > > +                       compatible = "sifive,e24", "riscv";
> > > > > +                       reg = <2>;
> > > > > +                       device_type = "cpu";
> > > > > +                       i-cache-block-size = <32>;
> > > > > +                       i-cache-sets = <256>;
> > > > > +                       i-cache-size = <16384>;
> > > > > +                       riscv,isa = "rv32imafc";
> > > > > +                       status = "disabled";
> > > > > +
> > > > > +                       cpu2_intc: interrupt-controller {
> > > > > +                               compatible = "riscv,cpu-
> > > > > intc";
> > > > > +                               interrupt-controller;
> > > > > +                               #interrupt-cells = <1>;
> > > > > +                       };
> > > > > +               };
> > > > > +
> > > > >                 cpu-map {
> > > > >                         cluster0 {
> > > > >                                 core0 {
> > > > > @@ -76,6 +93,10 @@ core0 {
> > > > >                                 core1 {
> > > > >                                         cpu = <&U74_1>;
> > > > >                                 };
> > > > > +
> > > > > +                               core2 {
> > > > > +                                       cpu = <&E24>;
> > > > > +                               };
> > > > 
> > > > Sorry but I think this change makes the topology more
> > > > inaccurate.
> > > > 
> > > > The E24 core is very independent, just another CPU core
> > > > connected
> > > > the
> > > > same bus -- even no coherency (E24 takes AHB, which is not
> > > > coherency-
> > > > sensible). Even the TAP of it is independent with the U74 TAP.
> > > > 
> > > > And by default it does not boot any proper code (if a debugger
> > > > is
> > > > attached, it will discover that the E24 is in consistently
> > > > fault at
> > > > 0x0
> > > > (mtvec is 0x0 and when fault it jumps to 0x0 and fault again),
> > > > until
> > > > its clock is just shutdown by Linux cleaning up unused clocks.)
> > > > 
> > > > Personally I think it should be implemented as a remoteproc
> > > > instead.
> > > 
> > > Maybe I am missing something, but I don't quite get what the
> > > detail
> > > of how we access this in code has to do with the devicetree?
> > > It is added here in a disabled state, and will not be used by
> > > Linux.
> > > The various SiFive SoCs & SiFive corecomplex users that have a
> > > hart
> > > not capable of running Linux also have that hart documented in
> > > the
> > > devicetree.
> > > To me, what we are choosing to do with this hart does not really
> > > matter very much, since this is a description of what the
> > > hardware
> > > actually looks like.
> > 
> > The E24 is not in the core complex at all. It's just a dedicate CPU
> > connected to another bus (well as I saw the document says the E24
> > bus
> > is maximum 2G, I doubt whether it's the same bus with the U74 one).
> > 
> > The U74 MC only allows S5 management cores to be part of it, not
> > E24.
> 
> So is the correct topology more like:
> cpu-map {
>         cluster0 {
>                 core0 {
>                         cpu = <&U74_0>;
>                 };
>                 core1 {
>                         cpu = <&U74_1>;
>                 };
>         };
>         cluster1 {
>                 core0 {
>                         cpu = <&E24>;
>                 };
>         };
> };

Considering E24 seems to see a total different bus connected to it, I
don't think it even proper to add it to cpus node.

And I don't think it has a hart id of 2, as your node describes.

>