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

[Sudeep Holla]

On 16/07/14 15:08, Arnd Bergmann wrote:
> On Wednesday 16 July 2014 18:42:22 Jassi Brar wrote:
> > On 16 July 2014 18:39, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > > On Wednesday 16 July 2014 18:35:33 Jassi Brar wrote:
> > > > On 16 July 2014 18:15, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > > > > On Wednesday 16 July 2014 18:07:04 Jassi Brar wrote:
> > > > > > On 16 July 2014 15:46, Arnd Bergmann <arnd@xxxxxxxx> 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.
> > OK. So how about we drop mbox-names altogether and expect client
> > driver to simply provide an index of the mbox needed?
>
> That would be fine with me, but I think a lot of people like
> the idea of identifying things by name, and are used to that
> from the other subsystems.
>
> Maybe you can leave the mbox-names property defined as 'optional'
> in the generic mbox binding but remove the code in Linux? That way
> we can always put it back at a later point without changing the
> binding in an incompatible way.
>
> Individual mailbox clients can mandate specific strings.

This sounds reasonable to me.

Regards,
Sudeep

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