linux-kernel - Re: [PATCH 1/2] dt-bindings: reset: Add bindings for basic reset controller

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Date:   Mon, 29 May 2017 11:09:19 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Joel Stanley <joel@....id.au>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Andrew Jeffery <andrew@...id.au>
Subject: Re: [PATCH 1/2] dt-bindings: reset: Add bindings for basic reset
 controller

Hi Joel,

On Fri, 2017-05-26 at 13:32 +1000, Joel Stanley wrote:
> This adds the bindings documentation for a basic single-register reset
> controller.
> 
> The bindings describe a single 32-bit register that contains up to 32
> reset lines, each deasserted by clearing the appropriate bit in the
> register.
>
> Signed-off-by: Joel Stanley <joel@....id.au>
> ---
>  .../devicetree/bindings/reset/reset-basic.txt      | 31 ++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/reset/reset-basic.txt
> 
> diff --git a/Documentation/devicetree/bindings/reset/reset-basic.txt b/Documentation/devicetree/bindings/reset/reset-basic.txt
> new file mode 100644
> index 000000000000..7341e04e7904
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/reset/reset-basic.txt
> @@ -0,0 +1,31 @@
> +Basic single-register reset controller
> +======================================
> +
> +This describes a generic reset controller where the reset lines are controlled
> +by single bits within a 32-bit memory location. The memory location is assumed
> +to be part of a syscon regmap.

There are a few more assumptions. First, that the reset line is asserted
by setting the corresponding bits, and that it is deasserted by clearing
them. Further, that the bits are not auto-clearing. And then, that the
same bit can be read back to provide the current reset line status.

> +Reset controller required properties:
> + - compatible: should be "reset-basic"
> + - #reset-cells: must be set to 1
> + - reg: reset register location within regmap
> +
> +Device node required properties:
> + - resets phandle
> + - bit number, counting from zero, for the desired reset line. Max is 31.
> +
> +Example:
> +
> +syscon {
> +	compatible = "syscon";
> +
> +	uart_rest: rest@0c {

The device node name should be "reset-controller", and leading zeroes
should be dropped from the address part:

	uart_rest: reset-controller@c {

> +		compatible = "reset-basic";

Maybe this is not necessary for the example, but the compatible should
contain a vendor/hardware specific string first.

> +		#reset-cells = <1>;
> +		reg = <0x0c>;
> +	};
> +}
> +
> +&uart {
> +	resets = <&uart_rest 0x04>;

I'd use decimal here.

regards
Philipp