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

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

Hi Cristian, Marek, all,

I am working with Marek on the same project.

> > While I was going through the SCMI spec, DEN0056F , page 209 , section "4.1
> > Shared memory based transport" , bullet • Completion interrupts, I found it
> > explicitly states:
> > 
> > "
> > This transport supports polling or interrupt driven modes of communication.
> > In interrupt mode, when the callee completes processing a message, it raises
> > an interrupt to the caller. Hardware support for completion interrupts is
> > optional.
> > "
> 
> Oh, yes...I knew that...it is just that till now, no systems were really
> ever developed that lacked the completion IRQ as a whole, it was, till now,
> more of a case of having the capability NOT to use it selectively at runtime
> and instead use polling when wanted (like for clock ops in ISR context)

So, I also read in the spec that completion irq is optional and wondered
why it was not possible to describe that in DT. And while we do strive
to get the SCP fixed alone for technical reasons (it is just better),
the spec doesn't actually require this, right? So, my suggestion for v2
is to reword the commit messages a little. More in the direction of
"support irqless implementations" rather than "support broken FW until
fixed". Or?

> I am not sure what is the reason why this only-polling scenario was never
> supported in the HW description, this indeed pre-dates my work on SCMI....
> ...I would/will check with Sudeep, when he's back, what are the reasons for
> this (if any)...

Cool, thank you. Looking forward to hear about it!

Happy hacking,

   Wolfram