Re: [PATCH v2 1/2] dt-bindings: usb: Document the Allwinner H6 DWC3 glue

[Samuel Holland <samuel@sholland.org>]

On 4/30/21 2:44 PM, Rob Herring wrote:
> On Thu, Apr 29, 2021 at 10:19:11PM -0500, Samuel Holland wrote:
>> The RST_BUS_XHCI reset line in the H6 affects both the DWC3 core and the
>> USB3 PHY. This suggests the reset line controls the USB3 IP as a whole.
>> Represent this by attaching the reset line to a glue layer device.
> 
> Does that really mean anything more than a shared reset? Doesn't the 
> reset code support shared resets?

Yes, shared resets are supported.

I don't know exactly what it means -- the hardware's platform
integration is not well documented. The vendor BSP groups the controller
+ PHY together as a single node/device, and enables resources all at
once, so it is not clear which resources belong to which part.

The hardware layout appeared to be similar to other platforms, so it
seemed reasonable that the binding should be similar as well. Only
unipher and hi3660 put the resets property in the snps,dwc3 node itself;
the vast majority of platforms put it one level higher. I don't know
which is more "correct".

The benefit of following the more common binding is that it allows
sharing the glue code. The downside is that it is a bit more
complicated, and the warning for "ranges;", which several other
platforms appear to have as well.

>>
>> Signed-off-by: Samuel Holland <samuel@sholland.org>
>> ---
>>  .../usb/allwinner,sun50i-h6-dwc3.yaml         | 75 +++++++++++++++++++
>>  1 file changed, 75 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/usb/allwinner,sun50i-h6-dwc3.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/usb/allwinner,sun50i-h6-dwc3.yaml b/Documentation/devicetree/bindings/usb/allwinner,sun50i-h6-dwc3.yaml
>> new file mode 100644
>> index 000000000000..936b5c74043f
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/usb/allwinner,sun50i-h6-dwc3.yaml
>> @@ -0,0 +1,75 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/usb/allwinner,sun50i-h6-dwc3.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Allwinner H6 DWC3 USB controller
>> +
>> +maintainers:
>> +  - Chen-Yu Tsai <wens@csie.org>
>> +  - Maxime Ripard <mripard@kernel.org>
>> +
>> +properties:
>> +  compatible:
>> +    const: allwinner,sun50i-h6-dwc3
>> +
>> +  "#address-cells": true
>> +
>> +  "#size-cells": true
>> +
>> +  ranges: true
>> +
>> +  resets:
>> +    maxItems: 1
>> +
>> +# Required child node:
>> +
>> +patternProperties:
>> +  "^phy@[0-9a-f]+$":
>> +    $ref: ../phy/allwinner,sun50i-h6-usb3-phy.yaml#
>> +
>> +  "^usb@[0-9a-f]+$":
>> +    $ref: snps,dwc3.yaml#
>> +
>> +required:
>> +  - compatible
>> +  - ranges
>> +  - resets
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
>> +    #include <dt-bindings/clock/sun50i-h6-ccu.h>
>> +    #include <dt-bindings/reset/sun50i-h6-ccu.h>
>> +
>> +    usb3: usb@5200000 {
>> +        compatible = "allwinner,sun50i-h6-dwc3";
>> +        #address-cells = <1>;
>> +        #size-cells = <1>;
>> +        ranges;
>> +        resets = <&ccu RST_BUS_XHCI>;
>> +
>> +        dwc3: usb@5200000 {
>> +            compatible = "snps,dwc3";
>> +            reg = <0x05200000 0x10000>;
>> +            interrupts = <GIC_SPI 26 IRQ_TYPE_LEVEL_HIGH>;
>> +            clocks = <&ccu CLK_BUS_XHCI>,
>> +                     <&ccu CLK_BUS_XHCI>,
>> +                     <&rtc 0>;
>> +            clock-names = "ref", "bus_early", "suspend";
>> +            dr_mode = "host";
>> +            phys = <&usb3phy>;
>> +            phy-names = "usb3-phy";
>> +        };
>> +
>> +        usb3phy: phy@5210000 {
>> +            compatible = "allwinner,sun50i-h6-usb3-phy";
>> +            reg = <0x5210000 0x10000>;
>> +            clocks = <&ccu CLK_USB_PHY1>;
>> +            resets = <&ccu RST_USB_PHY1>;
>> +            #phy-cells = <0>;
>> +        };
>> +    };
>> -- 
>> 2.26.3
>>