On Tue, 19 May 2015, Andrew Bresticker wrote:

Lee,

On Thu, May 14, 2015 at 10:38 AM, Andrew Bresticker
[off-list ref] wrote:

quoted

On Thu, May 14, 2015 at 12:40 AM, Lee Jones [off-list ref] wrote:

quoted

On Thu, 14 May 2015, Jon Hunter wrote:

quoted

Hi Lee,

On 13/05/15 15:39, Lee Jones wrote:

quoted

On Mon, 04 May 2015, Andrew Bresticker wrote:

quoted

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 <redacted>
Cc: Rob Herring <redacted>
Cc: Pawel Moll <redacted>
Cc: Mark Rutland <redacted>
Cc: Ian Campbell <redacted>
Cc: Kumar Gala <redacted>
Cc: Samuel Ortiz <sameo-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: Lee Jones <redacted>
---
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

quoted

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/.

quoted

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....

I was waiting to hear Thierry's thoughts.  However, I am unconvinced
that you need an MFD driver for this and refuse to take a shell (read
"pointless") one on an "if we ever ..." clause.

Will you break backwards capability though?  I'm not sure you will.
Old DTBs will still use 'simple-mfd' and probe the devices in the
normal way.  *If* you introduce an MFD driver at a later date then the
old DTB will miss out the *new* functionality, which is expected and
accepted.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog