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

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Message-ID: <CAL_JsqJZBbu+UXqUNdZwg-uv0PAsNg55026PTwhKr5wQtxCjVQ@mail.gmail.com>
Date:   Thu, 4 Mar 2021 14:02:23 -0600
From:   Rob Herring <robh@...nel.org>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michal Simek <monstr@...str.eu>, git <git@...inx.com>,
        Piyush Mehta <piyush.mehta@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devicetree@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH v2 1/2] dt-bindings: usb: misc: Add binding for Microchip
 usb5744 hub

On Wed, Feb 24, 2021 at 7:38 AM Michal Simek <michal.simek@...inx.com> wrote:
>
> Hi Rob,
>
> On 2/11/21 3:42 PM, Rob Herring wrote:
> > On Thu, Feb 11, 2021 at 3:35 AM Michal Simek <michal.simek@...inx.com> wrote:
> >>
> >> 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@...inx.com>
> >>>>
> >>>> Added dt binding for usb5744 driver.
> >>>>
> >>>> Signed-off-by: Piyush Mehta <piyush.mehta@...inx.com>
> >>>> Signed-off-by: Michal Simek <michal.simek@...inx.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@...inx.com>
> >>>> +  - Michal Simek <michal.simek@...inx.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
> >
> > Yes, there are examples of how we don't want to do it.
>
> ok.
>
> >
> >> 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?
> >
> > See usb/usb-device.txt. And there is this[1] under review.
> >
> > For these cases with I2C, I'd really rather see the hub always under
> > the USB bus with a link to the I2C bus when connected.
>
> I read that thread and also looked at his device and it is very similar
> to this one. Binding should also have information about i2c or spi. It
> is the same case here that you can use this hub without any bus
> connected which works in default mode. Or when i2c/smbus is connected
> and the hub is waiting for initialization sequence. And I expect spi
> behaves very similarly but don't have this setup here.
>
> Do we have any binding doc which is using suggested bus link?

'i2c-bus' or 'ddc-i2c-bus' properties for I2C. Don't think we have
anything for SPI, but I'd expect it would be similar though we'd need
a cell for the chip-select.

Rob