Re: Using the mailbox subsystem for plain doorbells?

[Stephen Warren]

On 05/09/2016 09:29 PM, Jassi Brar wrote:
> On Tue, May 10, 2016 at 5:15 AM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
> > Jassi,
> >
> > Does the HW described below sound like something that should be represented
> > using the Linux kernel's mailbox subsystem, and related DT bindings? I think
> > the existing drivers/mailbox/pcc.c is similar, but wanted to double-check.
> >
> > We have some HW that literally just allows a SW-generated interrupt to be
> > generated by our main CPU complex to an auxiliary CPU, and likewise a
> > different interrupt can be generated in the opposite direction. There's no
> > ability to transfer any data; just an IRQ is generated. Our current mailbox
> > implementation just handles IRQ generation/reception so struct
> > mbox_chan_ops.send_data completely ignores the data parameter, and our IRQ
> > handler "receives" hard-coded NULL messages when the IRQ fires. Higher level
> > protocol code (using shared memory along with the plain-IRQ mbox channels)
> > is outside the mailbox driver.
> >
> > Does that fit the mailbox subsystem?
>  From the sound of it, yes.

Good to know, thanks.

> Some controllers need a mask/list of destination cpus, to which the
> irq is raised, written to some 'data' register. You too probably need
> to program the destination "id" in the controller? Maybe that should
> be done in send_data().

In this case, each mailbox communicates with a different remote CPU, and 
there's a separate register to communicate with each remote CPU. So, 
send_data() completely ignores the data parameter since everything is 
derived from the mailbox's identity.