Re: [PATCH v2 6/9] riscv: dts: bouffalolab: add the bl808 SoC base device tree

Conor Dooley
2022-12-05T10:30:27Z

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On Mon, Dec 05, 2022 at 04:17:59PM +0800, Icenowy Zheng wrote:
> 在 2022-11-30星期三的 01:21 -0600，Samuel Holland写道：
> > On 11/27/22 07:24, Jisheng Zhang wrote:
> > > Add a baisc dtsi for the bouffalolab bl808 SoC.
> > >
> > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > > ---
> > >  arch/riscv/boot/dts/bouffalolab/bl808.dtsi | 74
> > > ++++++++++++++++++++++
> > >  1 file changed, 74 insertions(+)
> > >  create mode 100644 arch/riscv/boot/dts/bouffalolab/bl808.dtsi
> > >
> > > diff --git a/arch/riscv/boot/dts/bouffalolab/bl808.dtsi
> > > b/arch/riscv/boot/dts/bouffalolab/bl808.dtsi
> > > new file mode 100644
> > > index 000000000000..f4b170ccc32e
> > > --- /dev/null
> > > +++ b/arch/riscv/boot/dts/bouffalolab/bl808.dtsi
> > > @@ -0,0 +1,74 @@
> > > +// SPDX-License-Identifier: (GPL-2.0+ or MIT)
> > > +/*
> > > + * Copyright (C) 2022 Jisheng Zhang <jszhang@kernel.org>
> > > + */
> > > +
> > > +#include <dt-bindings/interrupt-controller/irq.h>
> > > +
> > > +/ {
> > > +       compatible = "bouffalolab,bl808";
> > > +       #address-cells = <1>;
> > > +       #size-cells = <1>;
> > > +
> > > +       cpus {
> > > +               timebase-frequency = <1000000>;
> > > +               #address-cells = <1>;
> > > +               #size-cells = <0>;
> > > +
> > > +               cpu0: cpu@0 {
> > > +                       compatible = "thead,c906", "riscv";
> > > +                       device_type = "cpu";
> > > +                       reg = <0>;
> > > +                       d-cache-block-size = <64>;
> > > +                       d-cache-sets = <256>;
> > > +                       d-cache-size = <32768>;
> > > +                       i-cache-block-size = <64>;
> > > +                       i-cache-sets = <128>;
> > > +                       i-cache-size = <32768>;
> > > +                       mmu-type = "riscv,sv39";
> > > +                       riscv,isa = "rv64imafdc";
> > > +
> > > +                       cpu0_intc: interrupt-controller {
> > > +                               compatible = "riscv,cpu-intc";
> > > +                               interrupt-controller;
> > > +                               #address-cells = <0>;
> > > +                               #interrupt-cells = <1>;
> > > +                       };
> > > +               };
> > > +       };
> > > +
> > > +       xtal: xtal-clk {
> > > +               compatible = "fixed-clock";
> > > +               #clock-cells = <0>;
> > > +               /* This value must be overridden by the board */
> > > +               clock-frequency = <0>;
> > > +       };
> > > +
> > > +       soc {
> > > +               compatible = "simple-bus";
> > > +               ranges;
> > > +               interrupt-parent = <&plic>;
> > > +               dma-noncoherent;
> > > +               #address-cells = <1>;
> > > +               #size-cells = <1>;
> > > +
> > > +               uart0: serial@30002000 {
> >
> > It's unfortunate that the SDK/documentation calls this peripheral
> > both
> > UART0 and UART3. I don't know if we can/should put the "M0" and "D0"
> > bus
> > peripherals in the same DT; it seems like most of the "M0"
> > peripherals
> > are not accessible from the C906. But if we did, this would conflict
> > with the other UART0.
>
> They're accessible but their interrupts are not, and I think this is
> called d0_uart or uart3, but not uart0 at all.
>
> >
> > > +                       compatible = "bouffalolab,bl808-uart";
> > > +                       reg = <0x30002000 0x1000>;
> > > +                       interrupts = <20 IRQ_TYPE_LEVEL_HIGH>;
> > > +                       clocks = <&xtal>;
> >
> > There's a clock controller with a mux and a gate between the crystal
> > and the UART. I'm not sure what the policy is about adding "fake"
> > suppliers before the real supplier has a binding defined.
> >
> > Unfortunately, Bouffalolab threw everything and the kitchen sink into
> > the GLB register space, so that complicates defining the binding for
> > the clock/reset controller part.

I think it depends on how backwards/forwards compatible it's going to
be? If new kernel + old DT works then that's all that's "required",
right? Old kernel + new DT isn't going to work, but that's not required
AFAIU.

> >
> > > +                       status = "disabled";
> > > +               };
> > > +
> > > +               plic: interrupt-controller@e0000000 {
> > > +                       compatible = "thead,c900-plic";
>
> Using a single c900-plic here needs more discussion, I think.

Yah. Per the discussion on [1], I think I'd rather we avoided the single
c900-plic. Either a SoC-specific value, or "something" involving the
"openplic" naming is needed here.

Thanks,
Conor.

1 - https://lore.kernel.org/linux-riscv/20221121041757.418645-3-uwu@icenowy.me/

> > > +                       reg = <0xe0000000 0x4000000>;
> > > +                       interrupts-extended = <&cpu0_intc
> > > 0xffffffff>,
> >
> > The C906 PLIC has an M-mode context, so 0xffffffff is not correct.
> > This
> > should reference the M-mode external interrupt.
> >
> > > +                                             <&cpu0_intc 9>;
> > > +                       interrupt-controller;
> > > +                       #address-cells = <0>;
> > > +                       #interrupt-cells = <2>;
> > > +                       riscv,ndev = <64>;
> >
> > The SDK/documentation lists IRQ numbers up to BL808_IRQ_PDS == 82, so
> > this value should be at least that.
> >
> > Regards,
> > Samuel
> >
> > > +               };
> > > +       };
> > > +};

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