Message-ID: <9ec6c2c6-cf99-4c6e-8fc2-871716987c54@kernel.org>
Date: Tue, 4 Mar 2025 11:03:47 +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 04/03/2025 10:09, Ivaylo Ivanov wrote:
> On 3/4/25 09:21, Krzysztof Kozlowski wrote:
>> On 03/03/2025 18:18, Ivaylo Ivanov wrote:
>>> 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@...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?
>>>> 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
>> The entire point is that eUSB2 is connected to DWC3, no? That's exactly
>> how it is done for example on Qualcomm SoC. Otherwise you claim that
>> DWC3 controls one phy, which controls another phy which controls UTMI...
> 
> But where does the USBCON fit? Is it just a side controller? Why's it needed
> in the first place? This is what I don't understand.

I assume usbcon, so old usbdrd, is the second DWC3's phy, just like qcom
qmpphy.

> 
>>
>>> 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).
>> It is the first time you use argument that it represents how the
>> hardware is and this is what we actually disagree. It is not like that.
>> You do not have chain of phys. Just look at any USB 3.0 DRD DWC diagram
>> from any Samsung SoC: where would you squeeze these two phys in relation
>> to what is called there "USB 3.0 PHY" which would be the third phy (!!!).
> 
> Yeah, my point was that it was different from any previous design. Now,
> I don't know if it's actually theoretically possible to design it like so. It's
> hard to just guess how the hardware is designed without having access
> to die shots, documentations or even just schematics.
> 
> Let's make it clear now, the changes your request are to document USBCON
> in the existing exynos binding, as well as to correct all explanations of how
> this block functions, right?

No, not necessarily. If USBCON is entirely different device than USBDRD
(different register layout, different features), then go ahead with a
new binding.

I was questioning your chain of PHYs and this should be investigated.


Best regards,
Krzysztof

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