Re: [PATCH v2 1/2] dt-bindings: usb: misc: Add binding for Microchip usb5744 hub

[Michal Simek <michal.simek@xilinx.com>]

Hi Rob,

On 2/10/21 11:22 PM, Rob Herring wrote:
> On Tue, Feb 09, 2021 at 11:48:09AM +0100, Michal Simek wrote:
>> From: Piyush Mehta <piyush.mehta@xilinx.com>
>>
>> Added dt binding for usb5744 driver.
>>
>> Signed-off-by: Piyush Mehta <piyush.mehta@xilinx.com>
>> Signed-off-by: Michal Simek <michal.simek@xilinx.com>
>> ---
>>
>> Changes in v2: None
>>
>>  .../bindings/usb/microchip,usb5744.yaml       | 56 +++++++++++++++++++
>>  MAINTAINERS                                   |  1 +
>>  2 files changed, 57 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/usb/microchip,usb5744.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/usb/microchip,usb5744.yaml b/Documentation/devicetree/bindings/usb/microchip,usb5744.yaml
>> new file mode 100644
>> index 000000000000..fe222f6db81d
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/usb/microchip,usb5744.yaml
>> @@ -0,0 +1,56 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: "http://devicetree.org/schemas/usb/microchip,usb5744.yaml#"
>> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
>> +
>> +title: Bindings for the Microchip USB5744 4-port Hub Controller
>> +
>> +description:
>> +  Microchip’s USB5744 SmartHub™ IC is a 4 port, SuperSpeed (SS)/Hi-Speed (HS),
>> +  low power, low pin count configurable and fully compliant with the USB 3.1
>> +  Gen 1 specification. The USB5744 also supports Full Speed (FS) and Low Speed
>> +  (LS) USB signaling, offering complete coverage of all defined USB operating
>> +  speeds. The new SuperSpeed hubs operate in parallel with the USB 2.0
>> +  controller, so 5 Gbps SuperSpeed data transfers are not affected by slower
>> +  USB 2.0 traffic.
>> +
>> +maintainers:
>> +  - Piyush Mehta <piyush.mehta@xilinx.com>
>> +  - Michal Simek <michal.simek@xilinx.com>
>> +
>> +properties:
>> +  compatible:
>> +    const: microchip,usb5744
>> +
>> +  reg:
>> +    maxItems: 1
>> +    description: |
>> +      Specifies the i2c slave address, it is required and should be 0x2d
>> +      if I2C is used.
> 
> If I2C is not used, then this should be underneath the USB host as a USB 
> device. That also implies a different compatible string. I'd suggest you 
> just say I2C is required if that's your use.

We can't say that i2c is required because we have both cases. One is
really usb hub connected over i2c which at least requires to send one
smbus command to start operate. But it can be extended to add more
features - limit speeds, disable ports, etc.

And the second is really the same usb hub without i2c connected which
runs in default mode. But reset is required to ensure proper reset
sequence.
Hub also have external clock chip which is not handled now because it is
just crystal on the board but if you want I can also model it via fixed
clock and call clock enable for it.

It is the same use case as is with
Documentation/devicetree/bindings/usb/usb3503.txt

Can you please elaborate why different compatible string should be used?
It is still the same device and not quite sure why different compatible
string should be used.

Do you also want to example where this node is the part of usb node?

> 
> 'const: 0x2d' instead of maxItems is the schema to express the address 
> if fixed.

Will fix.

Thanks,
Michal