[PATCH] mailbox: Enable BCM2835 mailbox support

Stephen Warren swarren at wwwdotorg.org
Sat Oct 25 20:17:41 PDT 2014

On 10/24/2014 09:51 AM, Lee Jones wrote:
> On Fri, 24 Oct 2014, Lubomir Rintel wrote:
> Thanks for sending this to list, as you are aware a lot of the other
> platform drivers depend on this.
> FYI: I don't know much about the Mailbox FW, so I'll leave the
> functional review to the people who do.  This is going to be a coding
> stylesque review instead. 
>> Implement BCM2835 mailbox support as a device registered with the
>> general purpose mailbox framework. Implementation based on commits by
>> Lubomir Rintel [1], Suman Anna and Jassi Brar [2] on which to base the
>> implementation.

>> Cc: Stephen Warren <swarren at wwwdotorg.org>
>> Cc: Jassi Brar <jassisinghbrar at gmail.com>
>> Cc: Lee Jones <lee.jones at linaro.org>
>> Cc: linux-rpi-kernel at lists.infradead.org
>> Cc: linux-arm-kernel at lists.infradead.org
> As you're only sending a small patch-set, it's better to address the
> emails to these guys directly, rather than doing so in here.  Cc's in
> commit messages are good if there are only a few patches within a
> large set to be sent to different addresses.

It's very useful for a submitter so they can work out the desired
recipients once rather than repeating the process each time they run git

Perhaps the U-Boot patman tool might help; I believe it strips out such
tags when sending email, so you get the benefit of storing metadata in
the commit description locally, but it doesn't clutter the email that
actually gets sent.

> FWIW, you can drop Stephen and myself from Cc completely as we're both
> subscribed to the RPi list and it's very low volume, thus we're not
> likely to miss it.

Technically you're supposed to CC all the maintainers either way, to
make sure the message shows up in their mailbox. You're right the list
is low enough volume the message shouldn't be missed, but I de-dup
message to multiple lists, so if I forgot to make the RPi list match
higher than the ARM list match (which I admittedly haven't) I might miss
it without a Cc.

>> diff --git a/drivers/mailbox/bcm2835-mailbox.c b/drivers/mailbox/bcm2835-mailbox.c
>> new file mode 100644
>> index 0000000..5a37ac2
>> --- /dev/null
>> +++ b/drivers/mailbox/bcm2835-mailbox.c
>> @@ -0,0 +1,291 @@
>> +/*
>> + *  Copyright (C) 2010 Broadcom
>> + *  Copyright (C) 2013-2014 Lubomir Rintel
>> + *  Copyright (C) 2013 Craig McGeachie
> Better to put these in chronological order.
> Does the Copyright really belong to you?

Assuming Lubomir made any non-trival changes, he certainly can claim (c)
(on parts of the file at least).

>> + * Parts of the driver are based on:
>> + *  - arch/arm/mach-bcm2708/vcio.c file written by Gray Girling that was
> This doesn't seem very future-proof.
>> + *    obtained from branch "rpi-3.6.y" of git://github.com/raspberrypi/
>> + *    linux.git
> Drop all this please.
>> + *  - drivers/mailbox/bcm2835-ipc.c by Lubomir Rintel at
>> + *    https://github.com/hackerspace/rpi-linux/blob/lr-raspberry-pi/drivers/
>> + *    mailbox/bcm2835-ipc.c
>> + *  - documentation available on the following web site:
>> + *    https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface
> And this.  Please don't put links to external Git repos in drivers.

Hmmm. It can be quite useful to track down the history of the driver. If
not mentioned in the comment, it'd be useful to mention this all in the
commit description at least.

>> +	while (!(readl(mbox->regs + MAIL0_STA) & ARM_MS_EMPTY)) {
>> +		u32 msg = readl(mbox->regs + MAIL0_RD);
>> +		unsigned int chan = MBOX_CHAN(msg);
>> +
>> +		if (!mbox->channel[chan].started) {
>> +			dev_err(dev, "Reply on stopped channel %d\n", chan);
>> +			continue;
>> +		}
>> +		dev_dbg(dev, "Reply 0x%08X\n", msg);
> This file is riddled with dev_dbg() calls, which are great to have
> during development, but are of very little use once in production.
> They also make the place look untidy.  Please remove them.

They don't print at run-time unless debugging is enabled for this
driver. Admittedly some of the dev_dbg() aren't that useful, but I think
tracing the sent/received messages could be quite useful outside of the
initial mailbox driver development, e.g. so that every person developing
a driver that uses the mailbox functionality doesn't have to implement
their own mailbox tracing mechanism. Perhaps the mailbox core provides
this already though?

>> +static const struct of_device_id bcm2835_mbox_of_match[] = {
>> +	{ .compatible = "brcm,bcm2835-mbox", },
>> +	{},
>> +};
>> +MODULE_DEVICE_TABLE(of, bcm2835_mbox_of_match);
> If you don't depend on OF, you need to protect this.

I've never seen that protected before, but perhaps because I've only
worked on platforms where OF was unconditionally present. If this is an
issue, I think it'd be better if the driver depended on OF for now,
since there's no reason to expect the driver to work on a system without
OF, since bcm2835 should always have OF.

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