linux-kernel - Re: [RFC v3 07/12] dt-bindings: gpio: Add hardware-timestamp-engine property

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Message-ID: <Yaamd11lUfjnhCbz@robh.at.kernel.org>
Date:   Tue, 30 Nov 2021 16:32:23 -0600
From:   Rob Herring <robh@...nel.org>
To:     Dipen Patel <dipenp@...dia.com>
Cc:     thierry.reding@...il.com, jonathanh@...dia.com,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-gpio@...r.kernel.org, linus.walleij@...aro.org,
        bgolaszewski@...libre.com, warthog618@...il.com,
        devicetree@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [RFC v3 07/12] dt-bindings: gpio: Add hardware-timestamp-engine
 property

On Tue, Nov 23, 2021 at 11:30:34AM -0800, Dipen Patel wrote:
> Some GPIO controllers can timestamp GPIO lines in real time using
> hardware timestamp engine. The optional property is added to facilitate
> this feature.
> 
> The nvidia GPIO controller has hardware timestamp engine as a backend
> to timestamp its GPIO lines in a real time. This change set adds
> hardware-timestamp-engine property to reflect that fact.
> 
> Signed-off-by: Dipen Patel <dipenp@...dia.com>
> ---
>  Documentation/devicetree/bindings/gpio/gpio.txt           | 8 ++++++++
>  .../devicetree/bindings/gpio/nvidia,tegra186-gpio.txt     | 7 +++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
> index a8895d339bfe..c6ae2eaf5762 100644
> --- a/Documentation/devicetree/bindings/gpio/gpio.txt
> +++ b/Documentation/devicetree/bindings/gpio/gpio.txt
> @@ -167,6 +167,13 @@ left to right from the passed array. An incomplete array (where the number
>  of passed named are less than ngpios) will still be used up until the last
>  provided valid line index.
>  
> +Optionally, a GPIO controller may have a "hardware-timestamp-engine" property.
> +This specifies the timestamp engine node. The property is only useful if the
> +hardware timestamp engine (HTE) serves as a back-end to support hardware
> +timestamp GPIO lines in a real time and GPIO controller has dependency on the
> +engine. It will be up to GPIO controller and HTE provider drivers to figure out
> +the mapping between GPIO controller and HTE namespaces of a given GPIO line.

This needs to be added to schema instead (in dtschema).

I find the 'hardware-' part to be redundant. What other type of 
timestamp engine are we going to have in the h/w description?

> +
>  Example:
>  
>  gpio-controller@...00000 {
> @@ -180,6 +187,7 @@ gpio-controller@...00000 {
>  		"LED G", "LED B", "Col A", "Col B", "Col C", "Col D",
>  		"Row A", "Row B", "Row C", "Row D", "NMI button",
>  		"poweroff", "reset";
> +	hardware-timestamp-engine = <&hadrware_ts_engine_node>;
>  }
>  
>  The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
> diff --git a/Documentation/devicetree/bindings/gpio/nvidia,tegra186-gpio.txt b/Documentation/devicetree/bindings/gpio/nvidia,tegra186-gpio.txt
> index adff16c71d21..20f6c9e69839 100644
> --- a/Documentation/devicetree/bindings/gpio/nvidia,tegra186-gpio.txt
> +++ b/Documentation/devicetree/bindings/gpio/nvidia,tegra186-gpio.txt
> @@ -127,6 +127,12 @@ Required properties:
>              - 8: Active low level-sensitive.
>              Valid combinations are 1, 2, 3, 4, 8.
>  
> +Optional properties:
> +- hardware-timestamp-engine
> +    AON GPIO controller has timestamp engine which can hardware timestamp
> +    GPIO configured as input and IRQ. This property specifies hardware
> +    timestamp engine (HTE) device-tree node.
> +
>  Example:
>  
>  #include <dt-bindings/interrupt-controller/irq.h>
> @@ -162,4 +168,5 @@ gpio@...0000 {
>  	#gpio-cells = <2>;
>  	interrupt-controller;
>  	#interrupt-cells = <2>;
> +	hardware-timestamp-engine = <&tegra_hte_aon>;
>  };
> -- 
> 2.17.1
> 
>