Re: [PATCHv3 00/14] drivers: mailbox: framework creation

From: Andy Green
Date: Thu Apr 25 2013 - 19:51:49 EST

On 26/04/13 06:29, the mail apparently from Suman Anna included:

Hi -

3. Shareable/exclusive nature of a mailbox. If it is shareable, then
duplicating the behavior between clients is not worth it, and this
should be absorbed into the respective controller driver.

I think the mailbox should be exclusively held by a client. That makes
many things simpler. Also remote firmwares won't be always robust
enough to handle commands from different subsystems intermixed. The
API only has to make sure the mailbox_get/put operations are very

This might be the case for specific remotes where we expect only one
client driver to be responsible for talking to it, but for generic
offloading, you do not want to have this restriction. You do not want
peer clients to go through a single main client, as the latencies or the
infrastructure imposed by the main client may not be suitable for the
other clients. The stricter usecase here would be the shareable mailbox,
and if it is exclusive, as dictated by a controller or device property,
then so be it and things would get simplified for that controller/device.

Knowing why Jassi mentioned this, the situation is a bit different than what you replied to. There are in fact multiple client drivers that can asynchronously decide to initiate communication on the same mailbox. Some of the client need to perform multi-step sequencing and lock the mailbox for the duration.

Right now we can implement that by having a driver on top to mediate, Jassi is suggesting being able to do the client locking at your layer as a primitive will simplify things, not least get rid of the mediation driver. Your layer has concept of completion and notifier already so it seems it wouldn't take much more.


Andy Green | Fujitsu Landing Team Leader â Open source software for ARM SoCs | Follow Linaro -!/linaroorg -
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at