linux-kernel - RE: [PATCH v3 3/7] PCI: imx6: Fix the regulator dump when link never came up

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Date:   Fri, 29 Oct 2021 03:58:41 +0000
From:   Richard Zhu <hongxing.zhu@....com>
To:     Mark Brown <broonie@...nel.org>
CC:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: RE: [PATCH v3 3/7] PCI: imx6: Fix the regulator dump when link never
 came up

> -----Original Message-----
> From: Mark Brown <broonie@...nel.org>
> Sent: Thursday, October 28, 2021 7:50 PM
> To: Richard Zhu <hongxing.zhu@....com>
> Cc: Francesco Dolcini <francesco.dolcini@...adex.com>;
> l.stach@...gutronix.de; bhelgaas@...gle.com;
> lorenzo.pieralisi@....com; jingoohan1@...il.com;
> linux-pci@...r.kernel.org; dl-linux-imx <linux-imx@....com>;
> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> kernel@...gutronix.de
> Subject: Re: [PATCH v3 3/7] PCI: imx6: Fix the regulator dump when link
> never came up
> 
> On Thu, Oct 28, 2021 at 06:50:58AM +0000, Richard Zhu wrote:
> 
> > > I would be really surprised to see PCI hardware that was able to
> > > support a supply being physically absent, and this use of
> > > _is_enabled() is quite simply not how any of this is supposed to
> > > work in the regulator API even for regulators that can be optional.
> 
> > [Richard Zhu] Actually, this regulator is one GPIO fixed regulator.
> > Controlled by SW to turn on (GPIO high) or turn off (GPIO low) the
> supply.
> > In some boards designs, this supply might be always on(GPIO high).
> > So, in point of SW driver view, this regulator is optional.
> 
> No, it's not.  The regulator API supports the systems where the regualtor
> is always on perfectly well, the client driver should not need to do
> anything to support them.
[Richard Zhu] Hi Mark: Thanks for your explains.
To disable the regulator explicitly, is a part of power save of i.MX PCIe port
 usage when link is down.
Because that this regulator might not be present at all on some boards
 (e.x: powered directly when board is powered up), so this regulator is
 optional from SW view.
> 
> > > Perhaps it's not causing problems in this design but if the supply
> > > is ever shared with anything else then the software will run into
> trouble.
> > > There will also be problems with the error handling on a system
> > > where the regulator needs to be controlled.
> 
> > [Richard Zhu] This GPIO fixed regulator is only used by controller driver.
> > It makes sense to disable the enabled regulator when driver probe is
> failed.
> 
> The driver should undo any enables it did itself, it should not undo any
> enables that anything else did which means it should never be basing
> decisions on regulator_is_enabled().  While the regulator may not be
> shared in the particular board you're looking at it may be shared in other
> systems.
[Richard Zhu] Understood. Thanks.
Can I disabled this regulator in PCIe probe failure handler without the
 regulator_is_enabled() check?

BR
Richard