linux-kernel - Re: [PATCH v2 3/3] Revert "usb: common: usb-conn-gpio: Make VBUS supply optional"

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Message-ID: <1621993487.26501.19.camel@mhfsdcap03>
Date:   Wed, 26 May 2021 09:44:47 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Thierry Reding <treding@...dia.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Paul Cercueil <paul@...pouillou.net>,
        Lee Jones <lee.jones@...aro.org>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2 3/3] Revert "usb: common: usb-conn-gpio: Make VBUS
 supply optional"

On Tue, 2021-05-25 at 13:36 +0200, Thierry Reding wrote:
> On Mon, May 24, 2021 at 01:51:51PM +0800, Chunfeng Yun wrote:
> > On Fri, 2021-05-21 at 15:20 +0200, Thierry Reding wrote:
> > > On Wed, May 19, 2021 at 02:39:46PM +0800, Chunfeng Yun wrote:
> > > > Vbus is already an optional supply, if the vbus-supply is not
> > > > provided in DTS, will use a dummy regulator,
> > > 
> > > That statement is not entirely correct. The dummy regulator is
> > > substituted only if the supply is in fact not optional. The idea behind
> > > that is to allow DTS files that don't specify all required regulators to
> > > get away with it, based on the assumption that the supply is one of
> > > those always-on supplies that are often not described in DTS.
> > Yes, you are right.
> > But from the point of result, it indeed can help to handle the absent
> > regulator.
> > > 
> > > > the warning log is as below:
> > > > "supply vbus not found, using dummy regulator"
> > > 
> > > And the reason why we get that warning is to point out that the DTS has
> > > a bug and that it should be fixed (by adding a proper regulator to take
> > > the place of the dummy).
> > > 
> > > > This reverts commit 4ddf1ac79e5f082451cd549283d2eb7559ab6ca9.
> > > 
> > > But if you read the description of that commit, the purpose of that
> > > patch was in fact to make the supply completely optional in the case
> > > where we already have the VBUS supply specified for the USB port that
> > > the connector is parented to.
> > Could you please give an example you mentioned?
> 
> You can find examples of this in these:
> 
> 	arch/arm64/boot/dts/nvidia/tegra210-p2597.dtsi
> 	arch/arm64/boot/dts/nvidia/tegra210-p3450-0000.dts
> 	arch/arm64/boot/dts/nvidia/tegra186-p2771-0000.dts
> 
> > It seems prefer to provide vbus supply in connector instead of port
> > according to dt-binding
> 
> My recollection is that the above (or at least some of them) predate USB
> connectors.
> 
> It's possible that we could convert the above to have the VBUS supply
> listed in the connector instead of the port. However, since we have to
> preserve backwards compatibility with older device trees, we can't
> revert the commit anyway.
Got it, thanks a lot

> 
> Thierry