linux-kernel - RE: [PATCH 1/4] dt-bindings: watchdog: aspeed: Add property for WDT SW reset

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Message-ID:
 <TYZPR06MB5203836945655EBFF667417BB2442@TYZPR06MB5203.apcprd06.prod.outlook.com>
Date: Mon, 14 Oct 2024 09:58:52 +0000
From: Chin-Ting Kuo <chin-ting_kuo@...eedtech.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, "patrick@...cx.xyz"
	<patrick@...cx.xyz>, "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
	"linux@...ck-us.net" <linux@...ck-us.net>, "robh@...nel.org"
	<robh@...nel.org>, "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>, "joel@....id.au"
	<joel@....id.au>, "andrew@...econstruct.com.au"
	<andrew@...econstruct.com.au>, "linux-watchdog@...r.kernel.org"
	<linux-watchdog@...r.kernel.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-aspeed@...ts.ozlabs.org"
	<linux-aspeed@...ts.ozlabs.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "Peter.Yin@...ntatw.com" <Peter.Yin@...ntatw.com>,
	"Patrick_NC_Lin@...ynn.com" <Patrick_NC_Lin@...ynn.com>,
	"Bonnie_Lo@...ynn.com" <Bonnie_Lo@...ynn.com>, "DELPHINE_CHIU@...ynn.com"
	<DELPHINE_CHIU@...ynn.com>, BMC-SW <BMC-SW@...eedtech.com>, Aaron Lee
	<aaron_lee@...eedtech.com>
Subject: RE: [PATCH 1/4] dt-bindings: watchdog: aspeed: Add property for WDT
 SW reset

Hi Krzysztof,

> -----Original Message-----
> From: Krzysztof Kozlowski <krzk@...nel.org>
> Sent: Monday, October 14, 2024 2:53 PM
> Subject: Re: [PATCH 1/4] dt-bindings: watchdog: aspeed: Add property for WDT
> SW reset
> 
> On 14/10/2024 04:07, Chin-Ting Kuo wrote:
> > Hi Krzysztof,
> >
> > Thanks for the review.
> >
> >> -----Original Message-----
> >> From: Krzysztof Kozlowski <krzk@...nel.org>
> >> Sent: Monday, October 7, 2024 2:58 PM
> >> Subject: Re: [PATCH 1/4] dt-bindings: watchdog: aspeed: Add property
> >> for WDT SW reset
> >>
> >> On 07/10/2024 08:34, Chin-Ting Kuo wrote:
> >>> Add "aspeed,restart-sw" property to distinguish normal WDT reset
> >>> from system restart triggered by SW consciously.
> >>>
> >>> Signed-off-by: Chin-Ting Kuo <chin-ting_kuo@...eedtech.com>
> >>> ---
> >>>  .../bindings/watchdog/aspeed,ast2400-wdt.yaml         | 11
> >> +++++++++++
> >>>  1 file changed, 11 insertions(+)
> >>>
> >>> diff --git
> >>>
> a/Documentation/devicetree/bindings/watchdog/aspeed,ast2400-wdt.yaml
> >>>
> b/Documentation/devicetree/bindings/watchdog/aspeed,ast2400-wdt.yaml
> >>> index be78a9865584..6cc3604c295a 100644
> >>> ---
> >>>
> a/Documentation/devicetree/bindings/watchdog/aspeed,ast2400-wdt.yaml
> >>> +++ b/Documentation/devicetree/bindings/watchdog/aspeed,ast2400-wdt.
> >>> +++ ya
> >>> +++ ml
> >>> @@ -95,6 +95,17 @@ properties:
> >>>        array with the first word defined using the
> >>> AST2600_WDT_RESET1_*
> >> macros,
> >>>        and the second word defined using the AST2600_WDT_RESET2_*
> >> macros.
> >>>
> >>> +  aspeed,restart-sw:
> >>> +    $ref: /schemas/types.yaml#/definitions/flag
> >>> +    description: >
> >>
> >> Why >?
> >>
> >
> > ">" will be removed in the next patch series and the description
> > content will be concatenated after the colon, ":".
> >
> >>> +      Normally, ASPEED WDT reset may occur when system hangs or
> >> reboot
> >>> +      triggered by SW consciously. However, system doesn't know
> >>> + whether
> >> the
> >>> +      restart is triggered by SW consciously since the reset event flag is
> >>> +      the same as normal WDT timeout reset. With this property, SW
> >>> + can
> >>
> >> So DTS has this property and watchdog bites (timeout) but you will
> >> ignore it and claim that it was software choice?
> >>
> >
> > No. Normally, when WDT is enabled, a counter is also be enabled. When
> > the counter is equal to an expected value, timeout event occurs.
> > AST2600 hardware supports a SW mode, when a magic number is filled
> > into a specific register, WDT reset is triggered immediately without
> controlling the counter and the counter is not counted.
> > Thus, WDT timeout doesn't occur.
> 
> How is this a no?
> 

It is used to emphasize that the driver doesn’t ignore the timeout event
because the counter is not counted when SW mode is used and thus, no
timeout occurs.

> >
> >> This does not make much sense to me, at least based on this
> >> explanation
> >>
> >>> +      restart the system immediately and directly without wait for WDT
> >>> +      timeout occurs. The reset event flag is also different from
> >>> + the
> >> normal
> >>> +      WDT reset. This property is only supported since AST2600
> platform.
> >>
> >> Supported as drivers? How is this related? Or you mean hardware? Then
> >> property should be restricted there.
> >>
> >
> > It is a hardware supported function on AST2600. For platform
> > compatibility, without this property, all behaviors are the same as the
> previous generation platform, AST2500.
> >
> > This property may be removed in the next patch series with referring
> > to Rob suggestion
> 
> s/may/will/
> 

This property will be removed in the next patch series.

> > in the other reply. After checking with the major users, it is
> > feasible to remove this property and using SW reset by default when
> > the restart operation is triggered by SW deliberately on AST2600 platform.
> >
> 
> 

Best Wishes,
Chin-Ting