linux-kernel - RE: [PATCH 1/2] dt-bindings: firmware: arm,scmi: introduce property mbox-rx-timeout-ms

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Date: Mon, 1 Jul 2024 12:41:11 +0000
From: Peng Fan <peng.fan@....com>
To: Sudeep Holla <sudeep.holla@....com>, "robh@...nel.org" <robh@...nel.org>
CC: "Peng Fan (OSS)" <peng.fan@....nxp.com>, Cristian Marussi
	<cristian.marussi@....com>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor
 Dooley <conor+dt@...nel.org>, "arm-scmi@...r.kernel.org"
	<arm-scmi@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] dt-bindings: firmware: arm,scmi: introduce property
 mbox-rx-timeout-ms

Hi Rob, Sudeep

> Subject: Re: [PATCH 1/2] dt-bindings: firmware: arm,scmi: introduce
> property mbox-rx-timeout-ms
> 
> On Thu, Jun 27, 2024 at 11:17:49PM +0000, Peng Fan wrote:
> > > Subject: Re: [PATCH 1/2] dt-bindings: firmware: arm,scmi:
> introduce
> > > property mbox-rx-timeout-ms
> > >
> > > On Fri, Jun 21, 2024 at 08:46:57PM +0800, Peng Fan (OSS) wrote:
> > > > From: Peng Fan <peng.fan@....com>
> > > >
> > > > System Controller Management Interface(SCMI) firmwares might
> > > have
> > > > different designs by SCMI firmware developers. So the maximum
> > > receive
> > > > channel timeout value might also varies in the various designs.
> > > >
> > > > So introduce property mbox-rx-timeout-ms to let each platform
> > > > could set its own timeout value in device tree.
> > > >
> > > > Signed-off-by: Peng Fan <peng.fan@....com>
> > > > ---
> > > >  Documentation/devicetree/bindings/firmware/arm,scmi.yaml | 6
> > > ++++++
> > > >  1 file changed, 6 insertions(+)
> > > >
> > > > diff --git
> > > a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > > > b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > > > index 4d823f3b1f0e..d6cc2bf4c819 100644
> > > > ---
> a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > > > +++
> b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > > > @@ -121,6 +121,12 @@ properties:
> > > >        atomic mode of operation, even if requested.
> > > >      default: 0
> > > >
> > > > +  max-rx-timeout-ms:
> > > > +    description:
> > > > +      An optional time value, expressed in milliseconds,
> > > > + representing,
> > > on this
> > > > +      platform, the mailbox maximum timeout value for receive
> > > channel.
> > >
> > > "on this platform"? Doesn't every property apply to the given
> platform?
> >
> > Yeah, apply to all the use mailbox.
> >
> > >
> > > > +    default: 0
> > >
> > > 0 means no timeout or response is instant?
> >
> > I should use 30ms same as what the driver currently use.
> >
> 
> That sounds very wrong to me. The binding is independent of current
> driver behaviour. How the driver handles the case of default 0 value is
> different from what the default value in the DT means IMO. You can't
> just set a default value in the DT binding based on the current driver
> setting.
> 
> We can always say since it is optional, absence of it is what driver
> handles as 30ms. 0ms is impossible or incorrect value as transport
> involves some delay even if it is in terms of uS. So I prefer to set a value
> of > 0 in DT and make that a requirement.

How about this?
  max-rx-timeout-ms:                                                                                
    $ref: /schemas/types.yaml#/definitions/uint32                                                   
    description:                                                                                    
      An optional time value, expressed in milliseconds, representing the                           
      mailbox maximum timeout value for receive channel.                                            
    minimum: 1                                                                                      
    maximum: 5000

or?

  max-rx-timeout-ms:                                                                                
    description:                                                                                    
      An optional time value, expressed in milliseconds, representing the                           
      mailbox maximum timeout value for receive channel. The value should                           
      be a non-zero value if set.

Thanks,
Peng.
> 
> --
> Regards,
> Sudeep