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Date: Thu, 14 May 2015 08:40:58 +0100
From: Lee Jones <lee.jones@linaro.org>
To: Jon Hunter <jonathanh@nvidia.com>
Cc: Andrew Bresticker <abrestic@chromium.org>,
        Stephen Warren <swarren@wwwdotorg.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Alexandre Courbot <gnurou@gmail.com>, devicetree@vger.kernel.org,
        linux-tegra@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>,
        Samuel Ortiz <sameo@linux.intel.com>
Subject: Re: [PATCH v8 4/9] mfd: Add binding document for NVIDIA Tegra XUSB
Message-ID: <20150514074058.GA22418@x1>
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 <20150513143954.GA3394@x1>
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On Thu, 14 May 2015, Jon Hunter wrote:

> Hi Lee,
> 
> On 13/05/15 15:39, Lee Jones wrote:
> > On Mon, 04 May 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@chromium.org>
> >> Cc: Rob Herring <robh+dt@kernel.org>
> >> Cc: Pawel Moll <pawel.moll@arm.com>
> >> Cc: Mark Rutland <mark.rutland@arm.com>
> >> Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
> >> Cc: Kumar Gala <galak@codeaurora.org>
> >> Cc: Samuel Ortiz <sameo@linux.intel.com>
> >> Cc: Lee Jones <lee.jones@linaro.org>
> >> ---
> >> Changes from v7:
> >>  - Move non-shared resources into child nodes.
> >> New for v7.
> >> ---
> >>  .../bindings/mfd/nvidia,tegra124-xusb.txt          | 37 ++++++++++++++++++++++
> >>  1 file changed, 37 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..bc50110
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt
> >> @@ -0,0 +1,37 @@
> >> +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.
> >> + - reg: Must contain the base and length of the XUSB FPCI registers.
> >> + - ranges: Bus address mapping for the XUSB block.  Can be empty since the
> >> +   mapping is 1:1.
> >> + - #address-cells: Must be 2.
> >> + - #size-cells: Must be 2.
> >> +
> >> +Example:
> >> +--------
> >> +	usb@0,70098000 {
> >> +		compatible = "nvidia,tegra124-xusb";
> >> +		reg = <0x0 0x70098000 0x0 0x1000>;
> >> +		ranges;
> >> +
> >> +		#address-cells = <2>;
> >> +		#size-cells = <2>;
> >> +
> >> +		usb-host@0,70090000 {
> >> +			compatible = "nvidia,tegra124-xhci";
> >> +			...
> >> +		};
> >> +
> >> +		mailbox {
> >> +			compatible = "nvidia,tegra124-xusb-mbox";
> >> +			...
> >> +		};
> > 
> > This doesn't appear to be a proper MFD.  I would have the USB and
> > Mailbox devices probe seperately and use a phandle to point the USB
> > device to its Mailbox.
> > 
> > usb@xyz {
> > 	mboxes = <&xusb-mailbox, [chan]>;
> > };
> > 
> 
> I am assuming that Andrew had laid it out like this to reflect the hw
> structure. The mailbox and xhci controller are part of the xusb
> sub-system and hence appear as child nodes. My understanding is that for
> device-tree we want the device-tree structure to reflect the actual hw.
> Is this not the case?

Yes, the DT files should reflect h/w.  I have requested to see what
the memory map looks like, so I might provide a more appropriate
solution to accepting a pretty pointless MFD.

Two solutions spring to mind.  You can either call
of_platform_populate() from the USB driver, as some already do:

  drivers/usb/dwc3/dwc3-exynos.c:
    ret = of_platform_populate(node, NULL, NULL, dev);
  drivers/usb/dwc3/dwc3-keystone.c:
    error = of_platform_populate(node, NULL, NULL, dev);
  drivers/usb/dwc3/dwc3-omap.c:
    ret = of_platform_populate(node, NULL, NULL, dev);
  drivers/usb/dwc3/dwc3-qcom.c:
    ret = of_platform_populate(node, NULL, NULL, qdwc->dev);
  drivers/usb/dwc3/dwc3-st.c:
    ret = of_platform_populate(node, NULL, NULL, dev);
  drivers/usb/musb/musb_am335x.c:
    ret = of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev);

Or use the "simple-mfd", which is currently in -next:

  git show next/master:Documentation/devicetree/bindings/mfd/mfd.txt

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