linux-kernel - Re: [PATCH v5 1/2] drivers/watchdog: Add optional ASPEED device tree properties

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Message-ID: <1501648105.29409.1.camel@aj.id.au>
Date:   Wed, 02 Aug 2017 13:58:25 +0930
From:   Andrew Jeffery <andrew@...id.au>
To:     Christopher Bostic <cbostic@...ux.vnet.ibm.com>, wim@...ana.be,
        linux@...ck-us.net, robh+dt@...nel.org, mark.rutland@....com,
        joel@....id.au, linux-watchdog@...r.kernel.org,
        devicetree@...r.kernel.org
Cc:     openbmc@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/2] drivers/watchdog: Add optional ASPEED device
 tree properties

On Mon, 2017-07-17 at 14:25 -0500, Christopher Bostic wrote:
> Describe device tree optional properties:
> 
>   * aspeed,reset-type = "cpu|soc|system|none"
>      One of three different, mutually exclusive, values
> 
> 	"cpu" : ARM CPU reset on signal
> 	"soc" : 'System on chip' reset
> 	"system" : Full system reset
> 
>      The value can also be set to "none" which indicates that no
>      reset of any kind is to be done via this watchdog.  This assumes
>      another watchdog on the chip is to take care of resets.
> 
>   * 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>
> ---
> v5 - Removed aspeed,interrupt property - no plans at this point to
>      need this functionality in the driver.
> v4 - Add aspeed-reset-type and assign one of four values,
>      cpu, soc, system, none.
> 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    | 32 ++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt b/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> index c5e74d7..2b34ce9 100644
> --- a/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> +++ b/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> @@ -8,9 +8,41 @@ Required properties:
>   - reg: physical base address of the controller and length of memory mapped
>     region
>  
> +Optional properties:
> +
> + - aspeed,reset-type = "cpu|soc|system|none"
> +
> +   Reset behavior - Whenever a timeout occurs the watchdog can be programmed
> +   to generate one of three different, mutually exclusive, types of resets.
> +
> +   Type "none" can be specified to indicate that no resets are to be done.
> +   This is useful in situations where another watchdog engine on chip is
> +   to perform the reset.
> +
> +   If 'aspeed,reset-type=' is not specfied the default is to enable system
> +   reset.
> +
> +   Reset types:
> +
> +        - cpu: Reset CPU on watchdog timeout
> +
> +        - soc: Reset 'System on Chip' on watchdog timeout
> +
> +        - system: Reset system on watchdog timeout
> +
> +        - none: No reset is performed on timeout. Assumes another watchdog
> +                engine is responsible for this.
> +
> + - 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.

Sorry I'm a little late on this one, but we should probably also add
some words to the effect that if you specify aspeed,external-signal,
then you also need to ensure the pinmux is configured for this to work.
For example in the devicetree we need to add:

    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_wdtrst1_default>;

Now the name of the pinctrl node isn't set in stone, so I don't think
we should mention it directly. However this is the essence of what we
want to describe.

Cheers,

Andrew

> + - aspeed,alt-boot:    If property is present then boot from alternate block.
> +
>  Example:
>  
> > >  	wdt1: watchdog@...85000 {
> >  		compatible = "aspeed,ast2400-wdt";
> >  		reg = <0x1e785000 0x1c>;
> > +		aspeed,reset-type = "system";
> > +		aspeed,external-signal;
> >  	};
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