linux-kernel - RE: [PATCH v1 1/3] dt-bindings: usb: Add HPE GXP UDCG Controller

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Date:   Wed, 23 Aug 2023 16:07:52 +0000
From:   "Yu, Richard" <richard.yu@....com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "Verdun, Jean-Marie" <verdun@....com>,
        "Hawkins, Nick" <nick.hawkins@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "conor+dt@...nel.org" <conor+dt@...nel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Chang, Clay" <clayc@....com>
Subject: RE: [PATCH v1 1/3] dt-bindings: usb: Add HPE GXP UDCG Controller


Thank you, Mr. Kozlowski.

>> I am implementing this driver using the Aspeed virtual hub driver as example. 
>> 
>> Just like the Aspeed virtual hub is in the Devicetree:
>> 
>> vhub: usb-vhub@...a0000 {
>> 	compatible = "aspeed,ast2600-usb-vhub";
>> 	reg = <0x1e6a0000 0x350>;
>> 	interrupts = <GIC_SPI 5 IRQ_TYPE_LEVEL_HIGH>;
>> 	clocks = <&syscon ASPEED_CLK_GATE_USBPORT1CLK>;
>> 	aspeed,vhub-downstream-ports = <7>;
>> 	aspeed,vhub-generic-endpoints = <21>;
>> 	pinctrl-names = "default";
>> 	pinctrl-0 = <&pinctrl_usb2ad_default>;
>> 	status = "disabled";
>> };
>> 
>> In my case:  (I am replacing "udcg" with "vhub" and remove the vehci reference).
>> 
>>  vhub: usb-vhub@...00800 {
>> 	compatible = "hpe,gxp-vhub";
>> 	reg = <0x80400800 0x0200>, <0x80401000 0x8000>;
>> 	reg-names = "vhub", "udc";
>> 	interrupts = <13>;
>> 	interrupt-parent = <&vic1>;
>> 	hpe,vhub-downstream-ports = <4>;
>> 	hpe,vhub-generic-endpoints = <16>;
>> };


> The hub is not virtual, it is real. I understand that it is some software block or FPGA, but still I propose to skip any references to virtual.

I will remove any references to "virtual" in comment and documentation.


>>>>> + hpe,vehci-downstream-ports:
>>>>> + description: Number of downstream ports supported by the GXP
>>>
>>>
>>>>> Why do you need this property in DT and what exactly does it represent?
>>>>> You have one device - EHCI controller - and on some boards it is 
>>>>> further customized? Even though it is the same device?
>>>>
>>>> That is correct. We can configure this VHUB Controller to have one 
>>>> to
>>>> 8 virtual ports. This is similar to the aspeed virtual USB HUB 
>>>> "aspeed,vhub-downstream-ports" moving forward in the next patch we 
>>>> are going to use "hpe,vhub-downstream-ports"
>> 
>>> Moving forward you need to address this lack of physical presence...
>>> Aren't these different devices and you just forgot to customize the compatible?
>> 
>> I don’t fully understand here. Isn't the lack of physical presence 
>> similar to the Aspeed virtual hub driver?
.
> I don't know Aspeed virtual hub driver. In any case, driver is irrelevant to the bindings.

> Why setting maximum number of downstream ports or devices would be needed per-board? 
> Do you save some resources that way?

That is correct. Each port/devices will have to allocate resources and create device descriptor entry.
Currently, I set the number of downstream ports to be 4. Thus, I will have:

/sys/bus/platform/devices/80400800.vhub/80400800.vhub:p1   <=== for kvm keyboard/mouse
/sys/bus/platform/devices/80400800.vhub/80400800.vhub:p2   <=== for virtual CD/DVD/ISO image
/sys/bus/platform/devices/80400800.vhub/80400800.vhub:p3   <=== for virtual USB key
/sys/bus/platform/devices/80400800.vhub/80400800.vhub:p4   <=== for virtual NIC

Just like aspeed:
In g5 (aspeed-g5.dtsi), aspeed,vhub-downstream-ports = <5>;
In g6 (aspeed-g6.dtsi), aspeed,vhub-downstream-ports = <7>;

> Best regards,
> Krzysztof

Thanks

Richard.