linux-kernel - Re: [PATCH 1/3] Documentation: dtb: xgene: Add hwmon dts binding documentation

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Date:	Tue, 7 Jun 2016 22:50:12 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Hoan Tran <hotran@....com>
Cc:	Rob Herring <robh@...nel.org>, Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Jonathan Corbet <corbet@....net>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Duc Dang <dhdang@....com>, Loc Ho <lho@....com>,
	linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Devicetree List <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/3] Documentation: dtb: xgene: Add hwmon dts binding documentation

On Tue, May 24, 2016 at 6:31 AM, Hoan Tran <hotran@....com> wrote:
> Hi Rob,
>
> Thanks for your review !
>
> On Mon, May 23, 2016 at 1:30 PM, Rob Herring <robh@...nel.org> wrote:
>>
>> On Mon, May 16, 2016 at 09:17:25AM -0700, Hoan Tran wrote:
>> > This patch adds the APM X-Gene hwmon device tree node documentation.
>> >
>> > Signed-off-by: Hoan Tran <hotran@....com>
>> > ---
>> >  .../devicetree/bindings/hwmon/apm-xgene-hwmon.txt          | 14 ++++++++++++++
>> >  1 file changed, 14 insertions(+)
>> >  create mode 100644 Documentation/devicetree/bindings/hwmon/apm-xgene-hwmon.txt
>> >
>> > diff --git a/Documentation/devicetree/bindings/hwmon/apm-xgene-hwmon.txt b/Documentation/devicetree/bindings/hwmon/apm-xgene-hwmon.txt
>> > new file mode 100644
>> > index 0000000..49a482e
>> > --- /dev/null
>> > +++ b/Documentation/devicetree/bindings/hwmon/apm-xgene-hwmon.txt
>> > @@ -0,0 +1,14 @@
>> > +APM X-Gene hwmon driver
>> > +
>> > +Hwmon driver accesses sensors over the "SLIMpro" mailbox.
>>
>> DT bindings describe h/w, not driver data.
> How about this description: "APM X-Gene SOC sensors are accessed over
> the "SLIMpro" mailbox" ?
>> I'm not sure this belongs in
>> DT and perhaps the devices for the mailbox should be created by the
>> mailbox driver.
> I don't think the current mailbox supports it.
>>
>> > +
>> > +Required properties :
>> > + - compatible : should be "apm,xgene-slimpro-hwmon"
>> > + - mboxes : use the label reference for the mailbox as the first parameter.
>> > +         The second parameter is the channel number.
>>
>> When do you expect this to be different mailbox numbers?
> No, this number is not changed. This "mboxes" property is used and
> required by mailbox.c when hwmon driver requests a mailbox channel
>
I think that's inaccurate.

The h/w and the firmware combined is the "platform" from Linux POV.
Channels are physical resources provided by a mailbox controller.
Currently the firmware listens on Channel-7 but some future revision
might switch to, say, Channel-9.  Or say the same firmware on next
revision of h/w may have to switch to Channel-3 because it has only 4
channels. So I see the mailbox channel number as a hardware property
just like an IRQ (which very often change with SoC iterations).

Cheers.