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

[Jon Hunter <jonathanh@nvidia.com>]

On 14/05/15 10:30, Lee Jones wrote:
> On Thu, 14 May 2015, Jon Hunter wrote:
>> On 14/05/15 08:40, Lee Jones wrote:
>>> On Thu, 14 May 2015, Jon Hunter wrote:
>>>> 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.
>>
>> For the xusb-host has memory from 0x7009000 - 0x7009ffff.
>>
>> Within this range, we have this fpci range which is defined as 0x7009800
>> - 0x70098fff. This range is being shared between the mailbox and xhci
>> drivers. Looking at the drivers, we have ...
>>
>> mailbox uses: 0x700980e0 - 0x700980f3 and 0x70098428 - 0x7009842b.
>> xhci uses:    0x70098000 - 0x700980cf and 0x70098800 - 0x70098803.
>>
>> So it is a bit messy as they overlap. However, we could have ...
>>
>> 	xusb_mbox: mailbox {
>> 		compatible = "nvidia,tegra124-xusb-mbox";
>> 		reg = <0x0 0x700980e0 0x0 0x14>,
>> 		      <0x0 0x70098428 0x0 0x4>;
>> 		...
>> 	};
>> 	usb-host@0,70090000 {
>> 		compatible = "nvidia,tegra124-xhci";
>> 		reg = <0x0 0x70090000 0x0 0x8000>,		      	
>> 		      <0x0 0x70098000 0x0 0x00d0>;
>> 		      <0x0 0x70098800 0x0 0x0004>;
>> 		      <0x0 0x70099000 0x0 0x1000>;
>> 		...
>> 	};
>>
>> I believe that Thierry and Stephen said that they wished to avoid
>> multiple devices sharing the same memory ranges, and so we would need to
>> divvy up the memory map as above. However, I am not sure if this is an
>> ok thing to do.
>> 	
>>> 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
>>
>> That is nice. Sounds like the "simple-bus" style of device but for an
> 
> That's precisely what it does.  FYI: You 'can' use "simple-bus" and it
> will do the right thing, but as an MFD isn't really a bus, it was
> decided to create something a little more fitting.
> 
>> mfd. Based upon the above, let me know if you think we could use the
>> "simple-mfd"?
> 
> I do. :)

Thanks Lee.

Thierry, any objections on the above mem-mapping?

Cheers
Jon