From mboxrd@z Thu Jan  1 00:00:00 1970
From: swarren@wwwdotorg.org (Stephen Warren)
Date: Thu, 19 Mar 2015 22:48:52 -0600
Subject: [PATCH 3/4 v4] mailbox: Enable BCM2835 mailbox support
In-Reply-To: <87619xq414.fsf@eliezer.anholt.net>
References: <1426213936-4139-1-git-send-email-eric@anholt.net>
 <1426213936-4139-3-git-send-email-eric@anholt.net>
 <5507A095.5090805@wwwdotorg.org> <87619xq414.fsf@eliezer.anholt.net>
Message-ID: <550BA6B4.3030604@wwwdotorg.org>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 03/18/2015 05:28 PM, Eric Anholt wrote:
> Stephen Warren <swarren@wwwdotorg.org> writes:
> 
>> On 03/12/2015 08:32 PM, Eric Anholt wrote:
>>> diff --git a/drivers/mailbox/bcm2835-mailbox.c
>>> b/drivers/mailbox/bcm2835-mailbox.c
>> 
>>> +#define MBOX_MSG(chan, data28)		(((data28) & ~0xf) | ((chan) &
>>> 0xf)) +#define MBOX_CHAN(msg)			((msg) & 0xf) +#define
>>> MBOX_DATA28(msg)		((msg) & ~0xf)
>> 
>> Even the concept of storing channel IDs in the LSBs feels like it
>> might be RPi-firmware-specific rather than HW-specific?
> 
> I guess?  If we found another firmware protocol, we could have
> that device's dt just specify a different compatible string.  But
> in the absence of another firmware to talk to, I'm not sure what
> you want here.

I would expect the mailbox driver to expose a single channel that just
transports 32-bit values, since the HW doesn't impose any kind of
structure on the values it transports AFAIK. Clients of the mailbox
driver would formulate the messages they send through the mailox using
the macros above.

I'm not sure whether the mailbox core allows multiple clients for the
same mailbox channel though? This HW appears to require it.

> Note that Roku's kernel code dump doesn't even communicate through
> the mailbox.  vcio.c exists, but is disconnected from the build.