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

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Message-ID: <20160429164448.GY3217@sirena.org.uk>
Date:	Fri, 29 Apr 2016 17:44:48 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
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 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.

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