linux-kernel - Re: [PATCH v2 1/2] drivers/watchdog: Add optional ASPEED device tree properties

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Date:   Wed, 28 Jun 2017 09:55:41 -0500
From:   Christopher Bostic <cbostic@...ux.vnet.ibm.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     wim@...ana.be, robh+dt@...nel.org, mark.rutland@....com,
        joel@....id.au, linux-watchdog@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] drivers/watchdog: Add optional ASPEED device tree
 properties



On 6/27/17 5:07 PM, Guenter Roeck wrote:
> On Tue, Jun 27, 2017 at 04:42:24PM -0500, Christopher Bostic wrote:
>>
>> On 6/27/17 4:32 PM, Guenter Roeck wrote:
>>> On Tue, Jun 27, 2017 at 04:17:33PM -0500, Christopher Bostic wrote:
>>>> Describe device tree optional properties:
>>>>
>>>>    * aspeed,arm-reet - ARM CPU reset on signal
>>>>    * aspeed,soc-reset - SOC reset on signal
>>>>    * aspeed,sys-reset - System reset on signal
>>>>            Disabling system reset may be required in situations where
>>>>            one of the other watchdog engines in the system is responsible
>>>>            for this.
>>>>    * 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>
>>>> ---
>>>> v2 - Add 'aspeed,' prefix to all optional properties
>>>>     - Add arm-reset, soc-reset, interrupt, alt-boot properties
>>>> ---
>>>>   .../devicetree/bindings/watchdog/aspeed-wdt.txt    | 25 ++++++++++++++++++++++
>>>>   1 file changed, 25 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt b/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
>>>> index c5e74d7..555b8b4 100644
>>>> --- a/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
>>>> +++ b/Documentation/devicetree/bindings/watchdog/aspeed-wdt.txt
>>>> @@ -8,9 +8,34 @@ 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 6 types of signals:
>>>> +
>>>> + - aspeed,arm-reset:  If property is present then reset ARM CPU only.
>>>> +
>>>> + - aspeed,soc-reset:  If property is present then reset SOC.
>>>> +
>>>> + - aspeed,sys-reset:  If property is present then reset the entire chip.
>>>> +                      In cases where one of the other watchdog engines
>>>> +                      in the system is responsible for system reset it
>>>> +                      may be required to not specify this property.
>>>> +
>>>> + - aspeed,interrupt:  If property is present then interrupt CPU.
>>>> +
>>>> + - aspeed,external-signal: If property is present then signal is sent to
>>>> +                           external reset counter (only WDT1 and WDT2).
>>>> + - aspeed,alt-boot:    If property is present then boot from alternate block.
>>>> +
>>>>   Example:
>>>>   	wdt1: watchdog@...85000 {
>>>>   		compatible = "aspeed,ast2400-wdt";
>>>>   		reg = <0x1e785000 0x1c>;
>>>> +		aspeed,arm-reset;
>>>> +		aspeed,soc-reset;
>>>> +		aspeed,sys-reset;
>>>> +		aspeed,interrupt;
>>>> +		aspeed,external-signal;
>>>> +		aspeed,alt-boot;
>>> Is that a bit mask or a value ? I would have thought that,
>>> for example, a complete system reset would include the SoC reset,
>>> and a SoC reset would include the ARM reset. Generating an
>>> interrupt while at the same time resetting the system (or
>>> part of it) doesn't seem to make much sense either.
>> No these aren't bitmasks.   The example was intended to indicate what could
>> be used.
>> In practice only a subset of each of these properties would make any sense.
>> How
>> would you suggest the example be formatted to convey that? Multiple examples
>> I suppose.
>>
> I would just pick one (which is perfectly fine). After all, it is an example.
>
> Reminds me: Is there a default (eg the chip's default configuration) ?
> In other words, what is expected to happen if none of the properties
> is specified ?
Default was to enable SOC reset (parameter aspeed,soc-reset)  and system 
reset (aspeed,sys-reset).  Based on your comments in patch v2 2/2 it 
would be necessary for backwards compatibility to preserve that default 
behavior.  So it seems the optional parameters should be inverted for 
these:   no-soc-reset, no-sys-reset.

Thanks,
Chris

> Thanks,
> Guenter
>