linux-kernel - Re: [PATCH v1 3/3] ARM64 LPC: update binding doc

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Date:	Thu, 14 Jan 2016 10:29:16 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Rongrong Zou <zourongrong@...il.com>, arnd@...db.de,
	catalin.marinas@....com, will.deacon@....com
Cc:	lijianhua@...wei.com, lixiancai@...wei.com, linuxarm@...wei.com,
	linux-kernel@...r.kernel.org, minyard@....org,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH v1 3/3] ARM64 LPC: update binding doc

On Tue, 2015-12-29 at 21:33 +0800, Rongrong Zou wrote:
> Signed-off-by: Rongrong Zou <zourongrong@...il.com>
> ---
>  .../devicetree/bindings/arm64/low-pin-count.txt      | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm64/low-pin-count.txt
> 
> diff --git a/Documentation/devicetree/bindings/arm64/low-pin-count.txt b/Documentation/devicetree/bindings/arm64/low-pin-count.txt
> new file mode 100644
> index 0000000..215f2c4
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm64/low-pin-count.txt
> @@ -0,0 +1,20 @@
> +Low Pin Count bus driver
> +
> +Usually LPC controller is part of PCI host bridge, so the legacy ISA
> +port locate on LPC bus can be accessed directly. But some SoC have
> +independent LPC controller, and we can access the legacy port by specifying
> +LPC address cycle. Thus, LPC driver is introduced.
> +
> +Required properties:
> +- compatible: "low-pin-count"

I'm not sure about the above. I'd rather just make it "isa" or maybe
isa-lpc. The LPC bus is fundamentally an ISA bus with the 3 cycle
types of ISA etc... I would also allow the node to be named "isa".

> +- reg: specifies low pin count address range
> +
> +
> +Example:
> +
> +        lpc_0: lpc@...b0000 {
> +		#address-cells = <1>;
> +		#size-cells = <1>;

As discussed earlier, address-cells should be 2 with the first cell
indicating the address space type (0 = mem, 1 = IO, possibly 2 =
firmware but that remains somewhat TBD).
 
> +                compatible = "low-pin-count";
> +                reg = <0x0 0xa01b0000 0x0 0x10000>;

And also as discussed, this is the business of the "ranges" property so
that children devices can be properly expressed.

> +        };

Also, this being a bus binding, it should describe the format for
children (for example, PNP related properties).

That leads to the obvious question: Why not just reference the existing
Open Firmware ISA binding ?

Cheers,
Ben.