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

[Krzysztof Kozlowski <krzk@kernel.org>]

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.

> 
> ...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