linux-kernel - Re: [RFT PATCH 1/3] usb: misc: usb3503: Fix HUB mode after bootloader initialization

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Date:	Mon, 02 May 2016 11:49:12 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Kukjin Kim <kgene@...nel.org>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-usb@...r.kernel.org,
	linux.amoon@...il.com, tjakobi@...h.uni-bielefeld.de,
	m.szyprowski@...sung.com, hverkuil@...all.nl,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [RFT PATCH 1/3] usb: misc: usb3503: Fix HUB mode after bootloader
 initialization

On 04/29/2016 06:44 PM, Mark Brown wrote:
> On Fri, Apr 29, 2016 at 01:55:14PM +0200, Krzysztof Kozlowski wrote:
>> On 04/29/2016 01:30 PM, Mark Brown wrote:
> 
>>> Supplies are only optional if they may be physically absent.  In this
>>> case it's possible that on device regulators may be used instead, a
>>> pattern more like that used for arizona-ldo1 where we represent those
>>> regulators might be better as it's more clearly describing the
>>> situation.  I'm just wondering if the supply lookup stuff there should
>>> be factored out as this is not an uncommon pattern..
> 
>>> It should at least be clearly stated what's going on, ignoring failure
>>> to get supplies is generally a bug and people will tend to blindly cut
>>> and paste things (witness all the breakage in graphics drivers with
>>> this).
> 
>> The VDD33 is really optional. The device can work in different
>> configuration, e.g. only on VBAT. How the reset logic would work then? I
>> don't know... I would suspect that it could be exactly the same (just
>> replace VDD33 with VBAT) but I am not sure.
> 
> What the Arizona example I mentioned does is look for the property
> specifying an external supply in DT and if there isn't one assumes that
> it must be using the internal regulator.  That's a bit icky but it does
> the right thing and is much simpler from a user point of view.

Okay, that indeed looks similar... in case of lack of external supplies
the usb3503 pins should be tied to the internal regulators.

However it seems I was wrong at the beginning. We've been looking here
at the schematics and the datasheet. The design is unfortunately a
little bit confusing but finally I think we got the impression how does
it work.

This VDD regulator supply actually is not a usb3503 USB HUB regulator
supply... but a supply to the LAN attached to this HUB. Regulator off/on
is needed for LAN to show up. The hub will show up with typical reset
(which is also missing before my patchset btw).

The LAN, as a USB device, is auto-probed so it cannot take the regulator
and play with it. The simplest idea I have is to add it as "external
supply"  to the parent: usb3503.

Best regards,
Krzysztof