linux-kernel - Re: [PATCH v2 3/8] dt-bindings: phy: add samsung,exynos2200-usbcon-phy schema file

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Message-ID: <4502b578-96e6-49e0-8f3b-54f6e5640c55@gmail.com>
Date: Sun, 2 Mar 2025 11:16:38 +0200
From: Ivaylo Ivanov <ivo.ivanov.ivanov1@...il.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I
 <kishon@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Alim Akhtar <alim.akhtar@...sung.com>,
 Philipp Zabel <p.zabel@...gutronix.de>, Abel Vesa <abel.vesa@...aro.org>,
 linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-samsung-soc@...r.kernel.org, linux-phy@...ts.infradead.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/8] dt-bindings: phy: add
 samsung,exynos2200-usbcon-phy schema file

On 2/25/25 10:11, Krzysztof Kozlowski wrote:
> On 24/02/2025 11:48, Ivaylo Ivanov wrote:
>> On 2/24/25 10:56, Krzysztof Kozlowski wrote:
>>> On Sun, Feb 23, 2025 at 02:22:22PM +0200, Ivaylo Ivanov wrote:
>>>> The Exynos2200 SoC has a USB controller PHY, which acts as an
>>>> intermediary between a USB controller (typically DWC3) and other PHYs
>>>> (UTMI, PIPE3). Add a dt-binding schema for it.
>>>>
>>>> Signed-off-by: Ivaylo Ivanov <ivo.ivanov.ivanov1@...il.com>
>>>> ---
>>>>  .../phy/samsung,exynos2200-usbcon-phy.yaml    | 76 +++++++++++++++++++
>>>>  1 file changed, 76 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/phy/samsung,exynos2200-usbcon-phy.yaml
>>> You have undocumented dependencies which prevent merging this file.
>>> First, dependencies have to be clearly expressed.
>> They are, in the cover letter.
> Where? I read it twice. Dependencies is the most important thing and
> should scream at beginning of the cover letter, so if you bury them
> somewhere deep it also would not matter - just like they were missing.
>
>>> Second, you should
>>> rather decouple the code from header dependencies, otherwise this cannot
>>> be merged for current release (just use clocks with long names, without IDs).
>> Sure
>
>>>> diff --git a/Documentation/devicetree/bindings/phy/samsung,exynos2200-usbcon-phy.yaml b/Documentation/devicetree/bindings/phy/samsung,exynos2200-usbcon-phy.yaml
>>>> new file mode 100644
>>>> index 000000000..7d879ec8b
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/phy/samsung,exynos2200-usbcon-phy.yaml
>>>> @@ -0,0 +1,76 @@
>>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>>> +%YAML 1.2
>>>> +---
>>>> +$id: http://devicetree.org/schemas/phy/samsung,exynos2200-usbcon-phy.yaml#
>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>> +
>>>> +title: Exynos2200 USB controller PHY
>>>> +
>>>> +maintainers:
>>>> +  - Ivaylo Ivanov <ivo.ivanov.ivanov1@...il.com>
>>>> +
>>>> +description:
>>>> +  Exynos2200 USB controller PHY is an intermediary between a USB controller
>>>> +  (typically DWC3) and other PHYs (UTMI, PIPE3).
>>> Isn't this the same as usbdrd phy? see: samsung,usb3-drd-phy.yaml
>> It's not (I think). There's a few reasons I've decided to make this separate
>> from the usb3-drd-phy bindings and exynos5-usbdrd driver:
>>
>> 1. This PHY does not provide UTMI and PIPE3 on its own. There's no tuning
> USBDRD phy does not provide UTMI and PIPE on its own either if you look
> at diagram - they call it phy controller.

Ughm. What? So in most exynos cases, there's a combination of multiple phys?

>
>> for them, and all that is needed from it is to disable HWACG, assert/
>> deassert reset and force bvalid/vbusvalid. After that SNPS eUSB2
>> initialization can be done and USB2 works. If the USBCON phy is not set
>> up before the eUSB2 one, the device hangs, so there is definitely a
>> dependancy between them. For PIPE3 we'd need to control the pipe3
>> attaching/deattaching and then initialize the synopsys USBDP combophy.
> Does it mean there is no USB DRD phy controller as before?
>
> Anyway the problem is you have DWC3 -> PHY -> PHY. Looks one phy too many.

So...

DWC3 -> USBDRD (USBCON) -> PHYs?

...with usbdrd controller connecting and controlling the USB2 and USB3
phys, as well as dual role mode? Well, where is the DRD part in the exynos5
driver?

I guess it does perfectly fit the job of a usbdrd controller then (if it
even deals with DRD). But then again,  this brings up two questions:
1. Should this driver even be named exynos2200-usbcon and not, for
example, exynos2200-usbdrd?
2. Are the exynos5-usbdrd phys really only USBDRD, or do they implement
USB speed functionality? What is the UTMI/PIPE3 setup for then?

ps: dealing with this without any documentations sucks.

Best regards,
Ivaylo

>
>
>> 2. With the way it's modelled, we need to parse phandles from eUSB2 and
>> USBDP to the controller. Adding that to the usbdrd driver would be...
>> weird. It makes more sense to model it as a separate driver, because
>> it functions in a different way.
> Just to be clear: we don't talk about drivers here.
>
>
> Best regards,
> Krzysztof