linux-kernel - Re: [PATCH 1/2] Documentation: dt: reset: Add syscon reset binding

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Date:	Thu, 28 Jan 2016 21:22:00 -0600
From:	Rob Herring <robh@...nel.org>
To:	"Andrew F. Davis" <afd@...com>
Cc:	Philipp Zabel <p.zabel@...gutronix.de>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, Suman Anna <s-anna@...com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] Documentation: dt: reset: Add syscon reset binding

On Mon, Jan 25, 2016 at 01:02:43PM -0600, Andrew F. Davis wrote:
> Add syscon reset controller binding. This will hook to the reset
> framework and use syscon/regmap to set reset bits. This allows
> reset control of individual SoC subsytems and devices with
> memory-mapped reset registers in a common register memory
> space.
> 
> Signed-off-by: Andrew F. Davis <afd@...com>
> [s-anna@...com: revise the binding format]
> Signed-off-by: Suman Anna <s-anna@...com>
> ---
>  .../devicetree/bindings/reset/syscon-reset.txt     | 84 ++++++++++++++++++++++
>  1 file changed, 84 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/reset/syscon-reset.txt
> 
> diff --git a/Documentation/devicetree/bindings/reset/syscon-reset.txt b/Documentation/devicetree/bindings/reset/syscon-reset.txt
> new file mode 100644
> index 0000000..466378a
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/reset/syscon-reset.txt
> @@ -0,0 +1,84 @@
> +SysCon Reset Controller
> +=======================
> +
> +Almost all SoCs have hardware modules that require reset control in addition
> +to clock and power control for their functionality. The reset control is
> +typically provided by means of memory-mapped I/O registers. These registers are
> +sometimes a part of a larger register space region implementing various
> +functionalities. This register range is best represented as a syscon node to
> +allow multiple entities to access their relevant registers in the common
> +register space.
> +
> +A SysCon Reset Controller node defines a device that uses a syscon node
> +and provides reset management functionality for various hardware modules
> +present on the SoC.

This may be one of those cases that is too low level to put into DT.

> +
> +SysCon Reset Controller Node
> +============================
> +Each of the reset provider/controller nodes should have the following
> +properties.
> +
> +Required properties:
> +--------------------
> + - compatible	: Should be "syscon-reset"
> + - syscon	: phandle to the syscon node containing the reset registers
> + - #reset-cells	: Should be 6. Please see the reset consumer node below for
> +                  usage details
> +
> +SysCon Reset Consumer Nodes
> +===========================
> +Each of the reset consumer nodes should have the following properties,
> +in addition to their own properties.
> +
> +Required properties:
> +--------------------
> + - resets	: A phandle and reset specifier pair, one pair for each reset
> +		  signal that affects the device, or that the device manages.
> +		  The phandle should point to the syscon node containing the
> +		  reset registers, and the reset specifier should have 6
> +		  cell-values. The reset specifier contains two similar pairs
> +		  of 3 cell-values each, the first of the pair containing the
> +		  reset control register information, and the second of the pair
> +		  containing the reset status register information. The reset
> +		  control and status registers can be same on some devices/SoCs.

What if there are no status bits?

> +
> +		  Each of the pairs of 3 cell-values should have the following
> +		  values:
> +		     Cell #1 : register offset of the reset control/status
> +		               register from the syscon register base
> +		     Cell #2 : bit shift value for the reset in the respective
> +		               reset control/status register
> +		     Cell #3 : polarity of the reset bit. Should be 1 for resets
> +		               that are asserted when the bit is set, 0 for
> +		               resets that are asserted when the bit is cleared
> +
> +Please also refer to Documentation/devicetree/bindings/reset/reset.txt for
> +common reset controller usage by consumers.
> +
> +
> +Example:
> +--------
> +The following example demonstrates a syscon node, the reset controller node
> +using the syscon node, and a consumer (a DSP device) on the TI Keystone 2
> +Hawking SoC.
> +
> +/ {
> +	soc {
> +		psc: power-sleep-controller@...50000 {
> +			compatible = "syscon";
> +			reg = <0x02350000 0x1000>;
> +		};
> +
> +		pscrst: psc-reset {
> +			compatible = "syscon-reset";
> +			syscon = <&psc>;
> +			#reset-cells = <6>;
> +		};

Any reason not to make this a child of psc?

> +
> +		dsp0: dsp0 {
> +			...
> +			resets = <&pscrst 0xa3c 8 0 0x83c 8 0>;
> +			...
> +		};
> +	};
> +};
> -- 
> 2.7.0
>