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

From: Christopher Bostic
Date: Thu Jul 06 2017 - 15:27:53 EST

On 7/6/17 9:35 AM, Rob Herring wrote:
On Thu, Jun 29, 2017 at 08:04:17AM -0700, Guenter Roeck wrote:
On Thu, Jun 29, 2017 at 08:39:59AM -0500, Christopher Bostic wrote:

On 6/28/17 10:33 PM, Guenter Roeck wrote:
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
* aspeed,alt-boot - Boot from alternate block on signal

Signed-off-by: Christopher Bostic <cbostic@xxxxxxxxxxxxxxxxxx>
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
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
+Optional properties:
+ Signal behavior - Whenever a timeout occurs the watchdog can be
+ 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
+ Typcally used in tandem with 'aspeed-external-signal'
Is this correct ? As I understand the datasheet, it could also used in
tandem with
True, that should be documented. Will add that.
+ 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
As the aspeed watchdog driver exists prior to this change an SOC reset is
done by
default. In order to preserve backwards compatibility a missing optional
should result in default behavior. I however need to be able to specify
that SOC
reset be disabled in some way. This goes back to our discussion about why
ever want to disable SYSTEM reset in the first place. Same reasoning
applies for
SOC reset.

I would instead use four properties.

Per my response above I think it should remain as aspeed,no-soc-reset due to
backwards compatibility requirements.
The same can be accomplished with "aspeed,no-reset", which would avoid the, in
my opinion, awkward "no-{sys,soc}-reset" poperties.

aspeed,sys-reset (which is the default)
Again as per our discussion yesterday I need some way to specify how system
reset is to be done. For backwards compatibility, a lack of parameter here
result in a system reset being configured. Only way to indicate to the
that no system reset is to be done is to indicate 'no' system reset in the
Or "aspeed,no-reset".

This parameter seems ambiguous as we could be doing a 'no system reset'
or a 'no SOC reset' in theory.
{arm,soc,sys}-reset are mutually exclusive per datasheet, and there is a
separate configuration bit which enables the reset in the first place.
I don't see how that is ambiguous.

Anyway, I don't think we are making any progress here. Let's wait for
guidance from Rob.
I tend to agree with Guenter.

Maybe using the form 'aspeed,reset-type = "cpu|soc|system"' would be
more aligned to the type of reset being mutually exclusive.

OK I'll update to this method.