[Linaro-acpi] [RFC v2 1/3] Mailbox: Add support for ACPI

Ashwin Chaugule ashwin.chaugule at linaro.org
Tue Jun 24 10:55:42 PDT 2014

Hi Arnd,

On 06/24/2014 10:18 AM, Arnd Bergmann wrote:

> I think a model that's closer to the mailbox subsystem would imply
> that the common mailbox code (or the pcc driver itself) parses the
> PCCT table, while the slave driver only passes an index.

This is pretty close to what I have here:

The PCC mailbox version:


Here the pcc driver in /drivers/acpi/pcc.c is the PCC mailbox controller 
which parses the PCCT and /drivers/acpi/pcc-test.c is a sample PCC 
client that sends dummy PCC reads/writes.

The PCC + CPPC non-mailbox version:


Here, the CPPC is the PCC client driver which parses the CPC tables. The 
mailbox conversion for this stuff is a WIP. But it should give an idea 
of how PCC and PCC clients would work.

> Or even better, the slave driver would only pass a device pointer,
> from which the pcc driver can find the pcc_register_resource in
> the corresponding ACPI table. The name of that table can be the
> string you pass down to the mailbox API. I suspect there is some
> issue that makes this all break down though, but that would be
> a portable way to do this for both DT and ACPI:
> If we wanted to use DT with the same driver, we would put the
> name of the table containing pcc_register_resource into the
> mbox-names property, and that could get used to look up a
> reference to the pcc device, and to the other data that you
> have in pcc_register_resource and PCCT.

So I dont think we should worry about the PCC clients being used in the 
DT case, since the PCC and its client specification is very ACPI centric 
and platforms that want to use these drivers will need an ACPI based 
firmware anyway. Which is why I think having a separate PCC specific 
mbox API makes sense.

Something like what you suggested should work well for ACPI based platforms.

struct mbox_controller *
mbox_find_pcc_controller(char *name)
	list_for_each_entry(mbox, &mbox_cons, node) {
		if (mbox->name)
			if (!strncmp(mbox->name, name))
				return mbox;

	return -ENODEV;

int pcc_mbox_get_channel(struct mbox_client *cl,
		char *name, unsigned chan_id,
		struct mbox_chan **chan)
	struct mbox_controller *mbox;
	mbox = mbox_find_pcc_controller(name);

	if (!mbox) {
		pr_err("PCC mbox %s not found.\n", name);
		return -ENODEV;

	*chan = &mbox->chans[chan_id];
	return init_channel(*chan, cl);


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