Message-ID: <20170629150417.GA10226@roeck-us.net>
Date:   Thu, 29 Jun 2017 08:04:17 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Christopher Bostic <cbostic@...ux.vnet.ibm.com>
Cc:     wim@...ana.be, robh+dt@...nel.org, mark.rutland@....com,
        joel@....id.au, linux-watchdog@...r.kernel.org,
        devicetree@...r.kernel.org, openbmc@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] drivers/watchdog: Add optional ASPEED device tree
 properties

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
> >>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.
> 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
> >no-soc-reset.
> 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
> property
> 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
> we'd
> ever want to disable SYSTEM reset in the first place.  Same reasoning
> applies for
> SOC reset.
> 
> >I would instead use four properties.
> >
> >    aspeed,arm-reset
> >    aspeed,soc-reset
> 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
> would
> result in a system reset being configured.  Only way to indicate to the
> driver
> that no system reset is to be done is to indicate 'no' system reset in the
> optional
> parameter.

Or "aspeed,no-reset".

> >    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.

Guenter

> >
> >There should also be a note explaining that the above are mutually
> >exclusive.
> >
> OK, will add that.
> 
> >>+ - 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
> 
> Will fix.
> 
> Thanks,
> Chris
> >
> >>+ - 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;
> >>      };
> >>
> >
> 

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