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

Ivaylo Ivanov
2025-03-03T17:18:13Z

On 3/3/25 09:24, Krzysztof Kozlowski wrote:
> On 02/03/2025 10:16, Ivaylo Ivanov wrote:
>> 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@gmail.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@gmail.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?
> No, drop last phy. You just wrote the same as me - two phys, because
> usbdrd is the phy. In all existing designs there is no such controllable
> object from the point of view of operating system.

What? Per my understanding, the phy property should refer to whatever is
is connected to dwc3 UTMI. In this case it's the so-called USBDRD phy (called
usbcon in downstream). Considering that the eUSB2 IP definitely also has UTMI
that has to be connected to something, doesn't that mean we have clearly
separated hardware blocks? Now, I guess one could argue that this USBCON
hardware block could be classified as a syscon. But I don't see the problem
with the current binding description, nor the modelling, as it represents
how the hardware is (unless I've gotten it completely wrong).

Best regards,
Ivaylo

>
>> ...with usbdrd controller connecting and controlling the USB2 and USB3
>> phys, as well as dual role mode?
> Yes.
>
>> Well, where is the DRD part in the exynos5
>> driver?
> DRD? I believe it is part of DWC3, the same as in every other standard
> implementation of Synopsys DWC3.
>
>> 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?
> Are you sure we talk about the same thing? USBDRD is IP block in the
> Exynos and a device driver. Call your device as appropriate it is -
> based on datasheet or downstream sources.
>
>> 2. Are the exynos5-usbdrd phys really only USBDRD, or do they implement
>> USB speed functionality? What is the UTMI/PIPE3 setup for then?
> Dunno, I don't get what you mean by "exynos5-usbdrd phys really only
> USBDRD". USBDRD is just the name of the device.
>
> Best regards,
> Krzysztof