[1/2] dt-bindings: power: reset: document the QEMU RISC-V virt machine poweroff device

Add the binding for the trivial Qemu RISC-V poweroff mechanism, which is
just a single MMIO register exposed through the DT.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 .../power/reset/qemu-riscv-virt-poweroff.txt     | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt

On Thu, 07 Nov 2019 13:24:07 PST (-0800), Christoph Hellwig wrote:
> Add the binding for the trivial Qemu RISC-V poweroff mechanism, which is
> just a single MMIO register exposed through the DT.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  .../power/reset/qemu-riscv-virt-poweroff.txt     | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
>
> diff --git a/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt b/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
> new file mode 100644
> index 000000000000..80ff6fd4e3b7
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
> @@ -0,0 +1,16 @@
> +QEMU RISC-V virt machine poweroff device
> +
> +This is a device in Qemu that can signal successful or error exit
> +by writing two magic numbers to a trivial mmio register.
> +A Linux poweroff is implemented as successful exit.

There's a third value that reboots the system, but it's only implemented in 
qemu-4.2 (not released yet) and above.  It'll be 'compatible = "sifive,test1", 
"sifive,test0";' (or at least will be when I merge my patch to do so).

> +
> +Required Properties:
> +-compatible: "sifive,test0"
> +-reg: Specifies the physical address of the register
> +
> +Example:
> +
> +	test@100000 {
> +		compatible = "sifive,test0";
> +		reg = <0x100000 0x1000>;
> +	};

Reviewed-by: Palmer Dabbelt <palmer@dabbelt.com>

On Thu, 7 Nov 2019, Christoph Hellwig wrote:

> Add the binding for the trivial Qemu RISC-V poweroff mechanism, which is

There's nothing RISC-V specific here.  This IP isn't defined in the RISC-V 
specifications, or anything like that.  

Apparently it's a SiFive IP block which now has a virtual IP 
implementation in QEMU in hw/riscv/sifive_test.c.  But since there's 
nothing RISC-V specific about this IP block, any QEMU system, with any CPU 
implementation, should be able to use this virtual IP, and this Linux 
driver.

For these reasons, it's better if "RISC-V" is just removed from everywhere 
in this driver.  If something needs to go in its place, "SiFive" may be 
better.


- Paul


> just a single MMIO register exposed through the DT.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  .../power/reset/qemu-riscv-virt-poweroff.txt     | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
> 
> diff --git a/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt b/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
> new file mode 100644
> index 000000000000..80ff6fd4e3b7
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
> @@ -0,0 +1,16 @@
> +QEMU RISC-V virt machine poweroff device
> +
> +This is a device in Qemu that can signal successful or error exit
> +by writing two magic numbers to a trivial mmio register.
> +A Linux poweroff is implemented as successful exit.
> +
> +Required Properties:
> +-compatible: "sifive,test0"
> +-reg: Specifies the physical address of the register
> +
> +Example:
> +
> +	test@100000 {
> +		compatible = "sifive,test0";
> +		reg = <0x100000 0x1000>;
> +	};
> -- 
> 2.20.1
> 
> 


- Paul

On Thu, Nov 07, 2019 at 02:32:01PM -0800, Paul Walmsley wrote:
> On Thu, 7 Nov 2019, Christoph Hellwig wrote:
> 
> > Add the binding for the trivial Qemu RISC-V poweroff mechanism, which is
>
> There's nothing RISC-V specific here.  This IP isn't defined in the RISC-V 
> specifications, or anything like that.  

Does the VM have a spec or anything? Would be nice if it did. Would be 
nicer still to just copy Arm's virt machine.

> Apparently it's a SiFive IP block which now has a virtual IP 
> implementation in QEMU in hw/riscv/sifive_test.c.  But since there's 
> nothing RISC-V specific about this IP block, any QEMU system, with any CPU 
> implementation, should be able to use this virtual IP, and this Linux 
> driver.
> 
> For these reasons, it's better if "RISC-V" is just removed from everywhere 
> in this driver.  If something needs to go in its place, "SiFive" may be 
> better.

IIRC, there's already syscon poweroff binding. You could probably use 
that.

> 
> 
> - Paul
> 
> 
> > just a single MMIO register exposed through the DT.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >  .../power/reset/qemu-riscv-virt-poweroff.txt     | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt b/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
> > new file mode 100644
> > index 000000000000..80ff6fd4e3b7
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/power/reset/qemu-riscv-virt-poweroff.txt
> > @@ -0,0 +1,16 @@
> > +QEMU RISC-V virt machine poweroff device
> > +
> > +This is a device in Qemu that can signal successful or error exit
> > +by writing two magic numbers to a trivial mmio register.
> > +A Linux poweroff is implemented as successful exit.
> > +
> > +Required Properties:
> > +-compatible: "sifive,test0"
> > +-reg: Specifies the physical address of the register
> > +
> > +Example:
> > +
> > +	test@100000 {
> > +		compatible = "sifive,test0";
> > +		reg = <0x100000 0x1000>;
> > +	};
> > -- 
> > 2.20.1
> > 
> > 
> 
> 
> - Paul