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

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Message-ID: <435f502c-1e1b-4d40-8dcc-34487905d69c@linaro.org>
Date: Mon, 15 Jan 2024 17:03:42 +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
Subject: Re: [PATCH 2/3] ASoC: dt-bindings: xmos,xvf3500: add bindings for
 XMOS XVF3500

On 15/01/2024 16:59, Javier Carrasco wrote:
>>> The voice data and any other information can be retrieved directly via
>>> USB from userspace. Once in normal operation, the device acts as a
>>> regular "onboard" USB device and the driver does not need to do any
>>> further management.
>>
>> So is this an USB device? If yes, then shouldn't be just auto-discovered
>> and you add here some bindings for other device? This looks like coding
>> power sequence not in USB node, but in some other, new node.
>>
>> Best regards,
>> Krzysztof
>>
> It is an USB device that requires two power supplies and a reset to
> boot. Afterwards it is auto-discovered and functions normally as a
> regular USB device. In that sense it works like the onboard USB HUBs:
> 
> https://github.com/torvalds/linux/blob/master/drivers/usb/misc/onboard_usb_hub.c
> 
> The onboard USB HUB driver is of course more complex because it has to
> support other features, but the idea of enabling the power supplies and
> toggling the reset signal is essentially the same.
> 

Yeah, about that... so this is not really correct device representation
for DT. There is no such device as XVF3500 outside of USB bus. There is
XVF3500 but on USB bus and this should be there. In the past we allowed
such root-level devices just because we did not have other way to handle
them. Now we have.

Best regards,
Krzysztof