Re: [PATCH v3 1/2] dt-bindings: firmware: arm,scmi: Document arm,no-completion-irq property

[Rob Herring <robh@kernel.org>]

On Thu, Jan 15, 2026 at 11:57:32AM +0000, Sudeep Holla wrote:
> On Thu, Jan 15, 2026 at 01:48:56AM +0100, Marek Vasut wrote:
> > Document new property arm,no-completion-irq, which sets all SCMI
> > operation into poll mode. This is meant to work around uncooperative
> > SCP implementations, which do not generate completion interrupts.
> > This applies primarily on mbox shmem based implementations.
> > 
> > With this property set, such implementations which do not generate
> > interrupts can be interacted with, until they are fixed to generate
> > interrupts properly.
> > 
> > Note that, because the original base protocol exchange also requires
> > some sort of completion mechanism, it is not possible to query SCMI
> > itself for this property and it must be described in DT. While this
> > does look a bit like policy, the SCMI provider is part of the
> > hardware, hence DT.
> > 
> > Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
> > ---
> > Cc: Conor Dooley <conor+dt@kernel.org>
> > Cc: Cristian Marussi <cristian.marussi@arm.com>
> > Cc: Florian Fainelli <florian.fainelli@broadcom.com>
> > Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> > Cc: Rob Herring <robh@kernel.org>
> > Cc: Sudeep Holla <sudeep.holla@arm.com>
> > Cc: arm-scmi@vger.kernel.org
> > Cc: devicetree@vger.kernel.org
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-renesas-soc@vger.kernel.org
> > ---
> > V2: s@mean@&t and limit poll transport to mailbox/shmem only
> > V3: - Reformat the commit message, expand property description to
> >       explicitly spell out this is hardware description.
> >     - Rename property from arm,poll-transport to arm,no-completion-irq
> > ---
> >  .../devicetree/bindings/firmware/arm,scmi.yaml        | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > index be817fd9cc34b..46d9a0a9a0e58 100644
> > --- a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > +++ b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > @@ -146,6 +146,14 @@ properties:
> >        this platform. If set, the value should be non-zero.
> >      minimum: 1
> >  
> > +  arm,no-completion-irq:
> > +    type: boolean
> > +    description:
> > +      An optional property which unconditionally forces polling in all transports,
> > +      meant for hardware which does not generate completion interrupts. This is
> > +      mainly meant to work around uncooperative SCP or SCP firmware, which does
> > +      not generate completion interrupts.
> > +
> 
> I would swap the order of the above two points.
> 
> “This optional property is intended for hardware that does not generate
> completion interrupts and can be used to unconditionally enable forced polling
> mode of operation.”
> 
> You need to update the commit message accordingly. We do not want to indicate
> how this property should be used, as that is left to the implementation. The
> emphasis should be on what this property indicates to its users.
> 
> Please update only if DT maintainers are also in agreement. I have just
> expressed my opinion. IIUC, it is aligned to standard DT binding rules but
> I may be wrong.

Makes sense to me.

With Sudeep's suggestion:

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>

Rob