Re: [PATCH v2 09/11] riscv: dts: add initial SOPHGO SG2042 SoC device tree

Conor Dooley
2023-09-21T10:15:39Z

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On Thu, Sep 21, 2023 at 05:56:28PM +0800, Chen Wang wrote:
> Regards,
>
> unicornx
>
> Conor Dooley <conor.dooley@microchip.com> 于2023年9月20日周三 16:58写道：
> >
> > Yo,
> >
> > On Wed, Sep 20, 2023 at 02:40:32PM +0800, Chen Wang wrote:
> > > Milk-V Pioneer motherboard is powered by SOPHON's SG2042.
> > >
> > > SG2042 is server grade chip with high performance, low power
> > > consumption and high data throughput.
> > > Key features:
> > > - 64 RISC-V cpu cores which implements IMAFDC
> >
> > That's not quite true though, is it?
>
> The cpu cores of SG2042 is c902 from T-HEAD, it supports vector, but
> it's v0.7, not official v1.0. If we declare it as supporting
> v-extension, the latest kernel(since 6.5) will issue rvv1.0
> instructions during booting and make c902 crash. So we have to remove
> "v" from the capability of ISA to pass the booting of machine. You can
> check the "riscv,isa = "rv64imafdc";" in DTS.

I know all of this, not my first rodeo looking at stuff using T-Head
cores ;)
What I meant was, imafdc is only a subset of what is supported,
there are other things like the T-Head bitmanip extensions too, right?
I'm not asking for it to be listed in the devicetree (yet), just
actually curious what else is on the c920 as I do not speak a language
that allows me to read the documentation for the cpu that I have been
able to find online.

> > > - 4 cores per cluster, 16 clusters on chip
> > > - ......
> >
> > What's a "....."? ;)
> I just cited a description from TRM of SG2042 and it looks too long. I
> will give a better description here and avoid using "......" in the
> next revision.
>
> >
> > >
> > > More info is available at [1].
> > >
> > > [1]: https://en.sophgo.com/product/introduce/sg2042.html
> >
> > Link: please.
> >
> > > Currently only support booting into console with only uart,
> > > other features will be added soon later.
> > >
> > > Acked-by: Xiaoguang Xing <xiaoguang.xing@sophgo.com>
> > > Signed-off-by: Xiaoguang Xing <xiaoguang.xing@sophgo.com>
> > > Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
> > > Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
> > > Signed-off-by: Chen Wang <wangchen20@iscas.ac.cn>
> >
> > There are 4 sign-offs here. Surely some of these should be
> > co-developed-bys?
> >
> > > + cpu0: cpu@0 {
> > > + compatible = "thead,c920", "riscv";
> > > + device_type = "cpu";
> > > + riscv,isa = "rv64imafdc";
> >
> > Please also add riscv,isa-base & riscv,isa-extensions.
> >
> > > + reg = <0>;
> > > + i-cache-block-size = <64>;
> > > + i-cache-size = <65536>;
> > > + i-cache-sets = <512>;
> > > + d-cache-block-size = <64>;
> > > + d-cache-size = <65536>;
> > > + d-cache-sets = <512>;
> > > + next-level-cache = <&l2_cache0>;
> > > + mmu-type = "riscv,sv39";
> > > +
> > > + cpu0_intc: interrupt-controller {
> > > + compatible = "riscv,cpu-intc";
> > > + interrupt-controller;
> > > + #interrupt-cells = <1>;
> > > + };
> > > + };
> >
> > > diff --git a/arch/riscv/boot/dts/sophgo/sg2042.dtsi b/arch/riscv/boot/dts/sophgo/sg2042.dtsi
> > > new file mode 100644
> > > index 000000000000..747fd9764c95
> > > --- /dev/null
> > > +++ b/arch/riscv/boot/dts/sophgo/sg2042.dtsi
> > > @@ -0,0 +1,439 @@
> > > +// SPDX-License-Identifier: GPL-2.0 OR MIT
> >
> > You should add () around the GPL-2.0 OR MIT.
> >
> > > +/*
> > > + * Copyright (C) 2022 Sophgo Technology Inc. All rights reserved.
> > > + */
> > > +
> > > +/dts-v1/;
> > > +#include <dt-bindings/interrupt-controller/irq.h>
> > > +
> > > +#include "sg2042-cpus.dtsi"
> > > +
> > > +#define SOC_PERIPHERAL_IRQ(nr) (nr)
> >
> > Why? What does this do? Where was it copied from?
> >
> It should be unnecessary， I will remove it in the next revision.
>
> > > +
> > > +/ {
> > > + compatible = "sophgo,sg2042";
> > > + #address-cells = <2>;
> > > + #size-cells = <2>;
> > > + dma-noncoherent;
> > > +
> > > + aliases {
> > > + serial0 = &uart0;
> > > + };
> > > +
> > > + /* the mem node will be updated by ZSBL. */
> >
> > huh? So these are random numbers below? Either put something useful here
> > or delete it please.
>
> The memory for SG2042 is not fixed, the bootloader will detect memory
> installed on board during booting and fill the actual address and size
> in the memory node. The comment " /* the mem node will be updated by
> ZSBL. */" is telling this.

Yes, I read the comment!

> We write memory nodes like this to make them act just as placeholders
> and the value is by default written as zero.

Why knowingly add something that is wrong, rather than omitting them
entirely?

Thanks,
Conor.

>
>
> >
> > > + memory@0 {
> > > + device_type = "memory";
> > > + reg = <0x00000000 0x00000000 0x00000000 0x00000000>;
> > > + };
> > > +
> > > + memory@1 {
> > > + device_type = "memory";
> > > + reg = <0x00000000 0x00000001 0x00000000 0x00000000>;
> > > + };
> > > +
> > > + memory@2 {
> > > + device_type = "memory";
> > > + reg = <0x00000000 0x00000002 0x00000000 0x00000000>;
> > > + };
> > > +
> > > + memory@3 {
> > > + device_type = "memory";
> > > + reg = <0x00000000 0x00000003 0x00000000 0x00000000>;
> > > + };
> >
> > > + soc: soc {
> > > + compatible = "simple-bus";
> > > + #address-cells = <2>;
> > > + #size-cells = <2>;
> > > + ranges;
> > > +
> > > + clint_mswi: interrupt-controller@7094000000 {
> > > + compatible = "sophgo,sg2042-clint-mswi", "thead,c900-clint-mswi";
> > > + reg = <0x00000070 0x94000000 0x00000000 0x00004000>;
> >
> > & nak to this without further explanation!
> >
> > Thanks,
> > Conor.
> >

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