linux-kernel - Re: [PATCH v3 1/2] drivers/watchdog: Add optional ASPEED device tree properties

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Date:   Wed, 28 Jun 2017 20:33:37 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Christopher Bostic <cbostic@...ux.vnet.ibm.com>, wim@...ana.be,
        robh+dt@...nel.org, mark.rutland@....com, joel@....id.au,
        linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, openbmc@...ts.ozlabs.org
Subject: Re: [PATCH v3 1/2] drivers/watchdog: Add optional ASPEED device tree
 properties

On 06/28/2017 05:28 PM, Christopher Bostic wrote:
> Describe device tree optional properties:
> 
>    * aspeed,arm-reet - ARM CPU reset on signal
>    * aspeed,no-soc-reset - SOC reset on signal
>    * aspeed,no-sys-reset - System reset on signal
>    * aspeed,interrupt - Interrupt CPU on signal
>    * aspeed,external-signal - Generate external signal (WDT1 and WDT2 only)
>    * aspeed,alt-boot - Boot from alternate block on signal
> 
> Signed-off-by: Christopher Bostic <cbostic@...ux.vnet.ibm.com>
> ---
> v3 - Invert soc and sys reset to 'no' to preserve backwards
>       compatibility.  SOC and SYS reset will be set by default
>       without any optional parameters set
> v2 - Add 'aspeed,' prefix to all optional properties
>     - Add arm-reset, soc-reset, interrupt, alt-boot properties
> ---
>   .../devicetree/bindings/watchdog/aspeed-wdt.txt    | 24 ++++++++++++++++++++++
>   1 file changed, 24 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt b/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> index c5e74d7..6f18005 100644
> --- a/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> +++ b/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> @@ -8,9 +8,33 @@ Required properties:
>    - reg: physical base address of the controller and length of memory mapped
>      region
>   
> +Optional properties:
> +   Signal behavior - Whenever a timeout occurs the watchdog can be programmed
> +   to generate/not generate 6 types of signals:
> +
> + - aspeed,arm-reset:	If property is present then reset ARM CPU only.
> +			If not specified no ARM CPU reset is done.
> +
> + - aspeed,no-soc-reset: If property is present then do not reset SOC.
> +			If not specified then SOC reset is done.
> +
> + - aspeed,no-sys-reset: If property is present then do not reset system.
> +			Typcally used in tandem with 'aspeed-external-signal'

Is this correct ? As I understand the datasheet, it could also used in tandem with
aspeed,interrupt.

> +			If not specified then system reset is done.
> +

I'll leave it up to Rob to decide, but for my part I don't understand no-soc-reset.
I would instead use four properties.

	aspeed,arm-reset
	aspeed,soc-reset
	aspeed,sys-reset (which is the default)
	aspeed,no-reset

There should also be a note explaining that the above are mutually exclusive.

> + - aspeed,interrupt:	If property is present then interrupt CPU.
> +			If not specified then don't interrupt CPU.
> +
> + - aspeed,external-signal: If property is present then signal is sent to
> +			external reset counter (only WDT1 and WDT2). If not
> +			specified no external signal is sent.

For consistency, either add an empty line here or remove the empty lines above

> + - aspeed,alt-boot:    If property is present then boot from alternate block.
> +
>   Example:
>   
>   	wdt1: watchdog@...85000 {
>   		compatible = "aspeed,ast2400-wdt";
>   		reg = <0x1e785000 0x1c>;
> +		aspeed,no-sys-reset;
> +		aspeed,external-signal;
>   	};
>