linux-kernel - Re: [v4, 1/2] drivers/watchdog: Add optional ASPEED device tree properties

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Date:   Mon, 10 Jul 2017 11:13:25 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Christopher Bostic <cbostic@...ux.vnet.ibm.com>
Cc:     mark.rutland@....com, devicetree@...r.kernel.org,
        linux-watchdog@...r.kernel.org, openbmc@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, wim@...ana.be, robh+dt@...nel.org
Subject: Re: [v4, 1/2] drivers/watchdog: Add optional ASPEED device tree
 properties

On Mon, Jul 10, 2017 at 10:07:40AM -0500, Christopher Bostic wrote:
> 
> 
> On 7/8/17 9:59 AM, Guenter Roeck wrote:
> >On Thu, Jul 06, 2017 at 07:48:59PM -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,interrupt - Interrupt CPU on signal
> >After thinking about that, I wonder if this is necessary. It could be
> >implied by providing an interrupt to the driver. The driver could then
> >set the interrupt configuration bit automatically.
> >
> >[ And the bit by itself doesn't really make sense if the driver doesn't
> >   also register an interrupt handler ]
> 
> The 'aspeed,interrupt' property was added for the sake of documenting all
> potential hardware configurations.  There is no plan as of now to enable
> this so I'm inclined to just remove this part from the documentation.  When
> and if this function is ever used the optional property can be documented at
> that time.
> 
Ok.

Thanks,
Guenter

> Thanks,
> Chris
> 
> >>   * 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>
> >>---
> >>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    | 35 ++++++++++++++++++++++
> >>  1 file changed, 35 insertions(+)
> >>
> >>diff --git a/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt b/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> >>index c5e74d7..f526b00 100644
> >>--- a/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> >>+++ b/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
> >>@@ -8,9 +8,44 @@ 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,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.
> >>+ - 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;
> >>  	};
>