Re: [PATCH v2 1/2] dt-bindings: firmware: arm,scmi: Document arm,poll-transport property

[Sudeep Holla <sudeep.holla@arm.com>]

On Fri, Jan 02, 2026 at 12:39:12PM +0100, Krzysztof Kozlowski wrote:
> On Wed, Dec 31, 2025 at 10:29:18PM +0100, Marek Vasut wrote:
> > Document new property arm,poll-transport, which sets all SCMI operation into
> 
> Please wrap commit message according to Linux coding style / submission
> process (neither too early nor over the limit):
> https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/process/submitting-patches.rst#L597
> 
> > 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
> > ---
> >  .../devicetree/bindings/firmware/arm,scmi.yaml         | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > index be817fd9cc34b..f4bf4173c5c7e 100644
> > --- a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > +++ b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> > @@ -146,6 +146,13 @@ properties:
> >        this platform. If set, the value should be non-zero.
> >      minimum: 1
> >  
> > +  arm,poll-transport:
> > +    type: boolean
> > +    description:
> > +      An optional property which unconditionally forces polling in all transports.
> > +      This is mainly meant to work around uncooperative SCP, which does not generate
> 
> Also not wrapped.
> 
> Anyway, you described the desired Linux feature or behavior, not the
> actual hardware. The bindings are about the latter, so instead you need
> to rephrase the property and its description to match actual hardware
> capabilities/features/configuration etc.
> 

I agree with this assessment. Rephrasing the property to reflect the actual
hardware/firmware characteristics makes more sense. Something along the lines
of `arm,no-completion-interrupt`, or a similar name, would better capture the
underlying reality, namely that the platform or firmware does not generate a
completion interrupt without encoding OS-specific policy or behavior.

-- 
Regards,
Sudeep