linux-kernel - Re: [PATCH V7 4/9] mfd: Add binding document for NVIDIA Tegra XUSB

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Message-ID: <CAL1qeaEYuWE6-ZbksGOhgjBbWkhkuo-k4c=6o4A2L67PrjYp2w@mail.gmail.com>
Date:	Thu, 30 Apr 2015 09:28:42 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Samuel Ortiz <sameo@...ux.intel.com>
Subject: Re: [PATCH V7 4/9] mfd: Add binding document for NVIDIA Tegra XUSB

On Thu, Apr 30, 2015 at 3:06 AM, Lee Jones <lee.jones@...aro.org> wrote:
> On Wed, 29 Apr 2015, Andrew Bresticker wrote:
>
>> On Wed, Apr 29, 2015 at 11:34 AM, Lee Jones <lee.jones@...aro.org> wrote:
>> > On Wed, 29 Apr 2015, Andrew Bresticker wrote:
>> >
>> >> Lee,
>> >>
>> >> On Wed, Apr 29, 2015 at 2:25 AM, Lee Jones <lee.jones@...aro.org> wrote:
>> >> > On Mon, 27 Apr 2015, Andrew Bresticker wrote:
>> >> >
>> >> >> Add a binding document for the XUSB host complex on NVIDIA Tegra124
>> >> >> and later SoCs.  The XUSB host complex includes a mailbox for
>> >> >> communication with the XUSB micro-controller and an xHCI host-controller.
>> >> >>
>> >> >> Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
>> >> >> Cc: Rob Herring <robh+dt@...nel.org>
>> >> >> Cc: Pawel Moll <pawel.moll@....com>
>> >> >> Cc: Mark Rutland <mark.rutland@....com>
>> >> >> Cc: Ian Campbell <ijc+devicetree@...lion.org.uk>
>> >> >> Cc: Kumar Gala <galak@...eaurora.org>
>> >> >> Cc: Samuel Ortiz <sameo@...ux.intel.com>
>> >> >> Cc: Lee Jones <lee.jones@...aro.org>
>> >> >> ---
>> >> >> New for v7.
>> >> >> ---
>> >> >>  .../bindings/mfd/nvidia,tegra124-xusb.txt          | 46 ++++++++++++++++++++++
>> >> >>  1 file changed, 46 insertions(+)
>> >> >>  create mode 100644 Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt
>> >> >>
>> >> >> diff --git a/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt
>> >> >> new file mode 100644
>> >> >> index 0000000..6a46680
>> >> >> --- /dev/null
>> >> >> +++ b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt
>> >> >> @@ -0,0 +1,46 @@
>> >> >> +NVIDIA Tegra XUSB host copmlex
>> >> >> +==============================
>> >> >> +
>> >> >> +The XUSB host complex on Tegra124 and later SoCs contains an xHCI host
>> >> >> +controller and a mailbox for communication with the XUSB micro-controller.
>> >> >> +
>> >> >> +Required properties:
>> >> >> +--------------------
>> >> >> + - compatible: For Tegra124, must contain "nvidia,tegra124-xusb".
>> >> >> +   Otherwise, must contain '"nvidia,<chip>-xusb", "nvidia,tegra124-xusb"'
>> >> >> +   where <chip> is tegra132.
>> >> >
>> >> > Okay.  Why?
>> >>
>> >> Why what?  This is the convention used for Tegra bindings and is also
>> >> documented in Documentation/devicetree/bindings/submitting-patches.txt.
>> >> See nvidia,tegra114-spi.txt and nvidia,tegra20-i2c.txt for other
>> >> examples of this.
>> >
>> > It seems strange to me that you'd mention two specific chips in one
>> > compatible string.  What's the purpose of that?
>>
>> The Tegra maintainers can correct me if I'm wrong here, but the point
>> is, I think, to future-proof the binding.  There are currently no
>> differences between Tegra124 and Tegra132 that need to be accounted
>> for in the driver, so the driver need only match against
>> "nvidia,tegra124-xusb".  If a Tegra132-specific quirk comes about
>> later all Tegra132 device-trees will also include the
>> "nvidia,tegra132-*" compatible string, so we can simply update the
>> driver without breaking DT backwards-compatibility.
>
> I still don't understand why you need to use them both at the same
> time.  Why don't you use nvidia,tegra124-* for Tegra124 and
> nvidia,tegra132-* for Tegra132?

The XUSB block on Tegra132 is identical to the one on Tegra124, so the
Tegra132 XUSB is 'compatible' with the Tegra124 XUSB.  Again, I'm just
following the convention the other Tegra bindings are using...

>> >> >> + - reg: Must contain register base and length for each register set listed
>> >> >> +   in reg-names.
>> >> >
>> >> > You've mentioned 2 of the cells, what about the remaining 2?
>> >>
>> >> The example given was for Tegra124, where there are two address cells
>> >> and two size cells.
>> >
>> > I don't get that.  How does that work?
>>
>> Tegra124 has a physical address space of > 4GB because of LPAE, thus a
>> single cell each for address and size is not sufficient.  The arm64
>> Tegra SoCs will obviously also use two address and size cells.  Take a
>> look at arch/arm/boot/dts/tegra124.dtsi.
>
> Okay, so these get shifted and &'ed into posstible 64bit addresses?

Yup.

-Andrew
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