Query about include/linux/mailbox.h

Hello,

At the end of all this, my question is should I put the BCM2835 mailbox driver in drivers somewhere, and try to make use of include/linux/mailbox.h, or should go with the view that mailbox drivers are inherently machine specific, have no common driver framework, and belongs in arch/arm/mach-bcm2835?

The background to this is that I'm trying to help bring Raspberry Pi support into the mainline kernel. Lubomir Rintel coded a mailbox driver
[1] that I liked the look off and want to fix up and push upstream. Stephen Warren suggested that Lubmir's patch had the benefit of using a new mailbox sub-system [2] and that I should have a look at that.

I've looked at include/linux/mailbox.h, and it only has 3 function declarations, which are all specific to the PL320. Unless there is something I've missed, then there is no mailbox sub-system to speak of.
Just a header file that will quickly a dependency nightmare.

I found a patch submission series from Jassi Brar [3] that looks like the start of an actual mailbox framework, but there is no indication of it in the current kernel source. I assume it was dropped for some reason.

I don't see much benefit to a mailbox sub-system. The BCM2835 one is quite a small piece of code, and I really see it as a machine-specific layer for other device drivers that implement a standard sub-system interface, like framebuffers.

Which all leads back to my opening question - which way do I jump? What I'd prefer to do is submit arch/arm/mach-bcm2835.c etc, and maybe even a patch to move include/linux/mailbox.h somewhere less inviting.

Cheers,
Craig.

[1]
http://lists.infradead.org/pipermail/linux-rpi-kernel/2013-April/000528.html
[2]
http://lists.infradead.org/pipermail/linux-rpi-kernel/2013-May/000546.html
[3] http://lkml.indiana.edu/hypermail/linux/kernel/1305.0/01978.html

It wasn't dropped.
Just the development was taken offline by the three of us I (for Fujitsu), Suman Anna (for TI) and Loic (for STE). Later we were joined by LF.Tan (for Intel). Please join us.
https://github.com/sumananna/mailbox/commits/jassiv3-3.10-omap should
be good to base on.

Thanks,
Jassi

So, this would be a good place to start?

https://github.com/sumananna/mailbox/commit/635c24eba19f67d1eb1ef7e7447f319c850b01e5#drivers/mailbox

See if I can get my head around that framework and what it does, and try fitting the BCM2835 mailbox into it?

Cheers,
Craig.

Yes. If you point me to your mailbox client drivers, I could also give it a look to see if we need some changes.

Regards
Jassi

This should be a reasonably concise view of things.

https://github.com/rickytarr/linux/commit/a9b131c63c73c450a567eb5fa527e8919e71bfd8

There is no header for the BCM2835 mailbox. At the point I started to add one, I learnt more about the multi-architecture approach to SoC code, and realised I'm going to have to rethink what I'm doing.

I don't think your code will need to change much, if at all. I'll try applying your patches and see what happens.

Cheers,
Craig.

Righty ho. This seems to be a reasonable attempt.

https://github.com/rickytarr/linux/tree/subsys-mailbox
https://github.com/rickytarr/linux/commit/e0c25371581d125e3f6a46f452ce3e95f1d267ee

It compiles cleanly and boots. Start with bcm2835_defconfig, and then enable Device Drivers -> Mailbox Hardware Support -> BCM 2835 Mailbox. I think it validates that BCM2835 mailbox support can fit into your generic device.

But that's as far as I know. I'm offering this as an early look only (comments and defects welcome). I've got to build something that uses it next. For all I know it might cause the Raspberry Pi to explode and vaporise any desk it is sitting on.

Out of interest, do you have a roadmap for moving this into the kernel mainline?

Cheers,
Craig.