linux-kernel - Re: [PATCH 2/3] ASoC: dt-bindings: xmos,xvf3500: add bindings for XMOS XVF3500

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Date: Mon, 22 Jan 2024 13:29:14 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Javier Carrasco <javier.carrasco@...fvision.net>,
 Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>
Cc: Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org,
 linux-usb@...r.kernel.org
Subject: Re: [PATCH 2/3] ASoC: dt-bindings: xmos,xvf3500: add bindings for
 XMOS XVF3500

On 16/01/2024 08:29, Javier Carrasco wrote:
> On 15.01.24 21:43, Krzysztof Kozlowski wrote:
>> On 15/01/2024 20:43, Javier Carrasco wrote:
>>> On 15.01.24 19:11, Krzysztof Kozlowski wrote:
>>>> On 15/01/2024 17:24, Javier Carrasco wrote:
>>>>> Do you mean that the XVF3500 should not be represented as a platform
>>>>> device and instead it should turn into an USB device represented as a
>>>>> node of an USB controller? Something like this (Rockchip SoC):
>>>>>
>>>>> &usb_host1_xhci {
>>>>> 	...
>>>>>
>>>>> 	xvf3500 {
>>>>> 		...
>>>>> 	};
>>>>> };
>>>>>
>>>>> Did I get you right or is that not the correct representation? Thank you
>>>>> again.
>>>>
>>>> I believe it should be just like onboard hub. I don't understand why
>>>> onboard hub was limited to hub, because other USB devices also could be
>>>> designed similarly by hardware folks :/
>>>>
>>>> And if we talk about Linux drivers, then your current solution does not
>>>> support suspend/resume and device unbind.
>>>>
>>>> Best regards,
>>>> Krzysztof
>>>>
>>>
>>> Actually this series is an attempt to get rid of a misuse of the
>>> onboard_usb_hub driver by a device that is not a HUB, but requires the
>>> platform-part of that driver for the initialization.
>>
>> That's just naming issue, isn't it?
>>
>>>
>>> What would be the best approach to provide support upstream? Should I
>>> turn this driver into a generic USB driver that does what the
>>> platform-part of the onboard HUB does? Or are we willing to accept
>>
>> No, because you did not solve the problems I mentioned. This is neither
>> accurate hardware description nor proper Linux driver model handling PM
>> and unbind.
>>
> You mentioned the PM handling twice, but I am not sure what you mean.
> The driver provides callbacks for SIMPLE_DEV_PM_OPS, which I tested in
> freeze and memory power states with positive results. On the other hand,
> I suppose that you insisted for a good reason, so I would be grateful if
> you could show me what I am doing wrong. The macro pattern was taken
> from other devices under sound/, which also check CONFIG_PM_SLEEP,
> but maybe I took a bad example or missed something.

You have two Linux devices: USB device and platform device. The platform
device controls power of USB device. If platform device goes to some
variant of sleep (PRM, system PM) before the USB device, how will USB
device react? Will it work? I doubt.

You have no ordering / dependencies / device links between these devices
thus possible problems.

>>> non-HUB devices in the onboard_usb_hub driver even though it supports
>>> more operations?
>>>
>>> I am adding linux-usb to this thread in case someone has other suggestions.
>>
>> I don't see any difference between this device and onboard hub. The
>> concept and the problem is the same. Therefore either treat it as as
>> onboard hub or come with USB-version of PCI power sequencing.
>>
> I have nothing against adding this device to onboard_usb_hub as long as
> it is valid upstream, so no conflicts arise with new additions to the
> list (which was the trigger for all of this with v6.7). That is

I am sorry, but we talk here only about upstream. I don't know therefore
what "valid upstream" means. You cannot send a patch which is "not valid
upstream". I mean, technically you can, but this would be waste of our
time and receive rather annoyed responses.

> obviously the most trivial solution and as you said, it is justs a
> naming issue because the power sequence is not HUB-specific.

I would ack it. Others? No clue, I also do not remember full story
behind onboard USB hub and why it was called "hub" instead of "onboard
USB device".

Best regards,
Krzysztof