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

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Message-ID: <c8184542-5dab-4403-bee4-867810397ae4@kernel.org>
Date: Tue, 25 Feb 2025 09:11:18 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Ivaylo Ivanov <ivo.ivanov.ivanov1@...il.com>
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 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.

> 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.


> 
> 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