Re: [PATCH v8 4/9] mfd: Add binding document for NVIDIA Tegra XUSB

Andrew Bresticker
2015-05-19T18:36:11Z

Lee,

On Thu, May 14, 2015 at 10:38 AM, Andrew Bresticker
<abrestic@chromium.org> wrote:
> On Thu, May 14, 2015 at 12:40 AM, Lee Jones <lee.jones@linaro.org> wrote:
>> 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.
>
> FWIW, the address map for XUSB looks like this:
>
> XUSB_HOST: 0x70090000 - 0x7009a000
> xHCI registers: 0x70090000 - 0x70098000
> FPCI configuration registers: 0x70098000 - 0x70099000
> IPFS configuration registers: 0x70099000 - 0x7009a000
>
>> 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);
>
> This still requires a small, separate driver to setup the regmap and
> do of_platform_populate(). The only difference is it lives in
> drivers/usb/ instead of drivers/mfd/.
>
>> Or use the "simple-mfd", which is currently in -next:
>>
>> git show next/master:Documentation/devicetree/bindings/mfd/mfd.txt
>
> I'm not too opposed to this, but Thierry was when I brought this up
> before. The issue here is that if we ever have to do something
> besides setting up a regmap in the MFD, we'd have to change the
> binding and break DT backwards-compatibility.

Any thoughts on this? A minimal MFD seems to be the best way to
future-proof this binding/driver should it need to be extended in the
future. If this is a firm NAK from you however, I'll need to let
Jassi now so that he can un-queue the mailbox patches for 4.2....

Thanks,
Andrew