Re: [PATCH v3 4/4] omap: mailbox: convert block api to kfifo

[Ohad Ben-Cohen <ohad@wizery.com>]

Hi Hiroshi,

On Mon, Jun 14, 2010 at 3:58 AM, Hiroshi DOYU <Hiroshi.DOYU@nokia.com> wrote:
> Does dspbridge really need its own defered work for sending mailbox
> messages?

We do, according to

http://permalink.gmane.org/gmane.linux.ports.arm.omap/38240

(thanks Rene for the explanation).

> For recieving, its defered work(tasklet) can be trigered directly in
> the above proposed callback, that callback can triger its own
> workqueue if necessary, then.

Agree

> I think that, for recieving, some PM
> command may has to be sent back immedieately inside of
> tasklet. omap_mbox_msg_send_sync() may handle this case.

Not sure how much QoS is an issue with mailbox (do we really have
latency issues ?), but I guess adding such interface can't hurt.

> I think that workqueue is only necessary when it has to sleep,
> otherwise tasklet is prefered.

I must say I disagree; tasklets are really not friendly to the whole
system's responsiveness and should be used only if really needed
(there was even an attempt to remove them entirely in the past:
http://lwn.net/Articles/239633/).

> I'd like to allow mutiple listners in some way, as the flexibility of
> mailbox functionalty.

This can be achieved using notifier chains of multiple listeners
callback, but I agree with Felipe: do we really want this
functionality ? I just rather not add code that no one is going to
use.

What do you say we start with enforcing only 1 listener and later, if
the use case of several listeners shows up, we'd add that support
(promise! :) ?

Thanks,
Ohad.