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

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Message-ID: <20150430100600.GC1815@x1>
Date:	Thu, 30 Apr 2015 11:06:00 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Andrew Bresticker <abrestic@...omium.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 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?

> >> >> + - 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?

I guess I just thought ARM64 addresses would look like:

  0xXXXXXXXXXXXXXXXX 0xXXXX

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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