Re: [Linaro-acpi] [PATCH v3 1/3] Mailbox: Add support for PCC mailbox and channels

[Arnd Bergmann <arnd@arndb.de>]

On Tuesday 02 September 2014 16:15:05 Ashwin Chaugule wrote:
> >
> >> > The "index" in mbox_request_channel() picks
> >> > up one set of strings. How should this work with PCC? Should we use
> >> > the PCC client platform_device->dev->platform_data to store mailbox
> >> > controller strings?
> >
> > I didn't think there was more than one PCC provider, why do you even
> > need a string?
> >
> > For the general case in ACPI, there should be a similar way of looking
> > up mailbox providers to what we have in DT, but if I understand you
> > correctly, the PCC specification does not allow that.
> 
> Right. At least not in a way DT does. PCC clients know if something
> needs to be written/read via PCC mailbox and can identify a PCC
> subspace. (i.e. Mailbox channel). The PCC mailbox is uniquely
> identified/defined in the spec.
> 
> #define ACPI_ADR_SPACE_PLATFORM_COMM    (acpi_adr_space_type) 10
> 
> So we could use this ID instead of a string and use that to look up
> the PCC controller for a PCC client.

I didn't realize this was the case. Does that mean we can treat
pcc as a linearly accessible address space the way we do for
system memory, pci-config etc?

If that works, we should probably just have a regmap for it rather
than expose the mailbox API to client drivers.

	Arnd