Re: [PATCHv8 2/2] mailbox: Introduce framework for mailbox

[Arnd Bergmann <arnd@arndb.de>]

On Wednesday 16 July 2014 18:35:33 Jassi Brar wrote:
> On 16 July 2014 18:15, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Wednesday 16 July 2014 18:07:04 Jassi Brar wrote:
> >> On 16 July 2014 15:46, Arnd Bergmann <arnd@arndb.de> wrote:
> >> > On Wednesday 16 July 2014 10:40:19 Sudeep Holla wrote:
> >> >> > +
> >> >> > +Required property:
> >> >> > +- mbox: List of phandle and mailbox channel specifier.
> >> >> > +
> >> >> > +- mbox-names: List of identifier strings for each mailbox channel
> >> >> > +               required by the client.
> >> >> > +
> >> >>
> >> >> IMO the mailbox names are more associated with the controller channels/
> >> >> mailbox rather than the clients using it. Does it make sense to move
> >> >> this under controller. It also avoid each client replicating the names.
> >> >
> >> > I think it would be best to just make the mbox-names property optional,
> >> > like we have for other subsystems.
> >> >
> >> A very similar subsystem - DMAEngine also has 'dma-names' as a
> >> required property.
> >>
> >> If a client is assigned only 1 mbox in DT, we can do without
> >> mbox-names. But I am not sure what to do if a client needs two or more
> >> differently capable mboxes? Simply allocating in order of mbox request
> >> doesn't seem very robust.
> >
> > Traditionally, these things (regs, interrupts, ...) are just accessed
> > by index. The reason why dmaengine requires the name is that some machines
> > can use multiple DMA engine devices attached to the same request line,
> > so the dmaengine subsystem can pick any of them that has a matching
> > name.
> And also, I think, when a client needs 2 different dma channels, say
> for RX and TX each. The api can't assign the first channel specified
> in 'dmas' property to the first channel request that comes to it,
> unless we assume client driver always requests dma channels in the
> order written in its DT node.  And this is the main reason I see for
> having mbox-names property.

Most subsystems require passing an explicit index in this case.

>   If we make mbox-names optional, do we assume client driver must
> request mbox in the order specified in its DT node?

Correct.

	Arnd