linux-kernel - RE: [PATCH v8 5/8] PCI: imx6: Refine the regulator usage

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Date:   Fri, 4 Mar 2022 08:44:51 +0000
From:   Hongxing Zhu <hongxing.zhu@....com>
To:     Francesco Dolcini <francesco.dolcini@...adex.com>
CC:     "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "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>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH v8 5/8] PCI: imx6: Refine the regulator usage

> -----Original Message-----
> From: Francesco Dolcini <francesco.dolcini@...adex.com>
> Sent: 2022年3月4日 15:46
> To: Hongxing Zhu <hongxing.zhu@....com>
> Cc: Francesco Dolcini <francesco.dolcini@...adex.com>;
> l.stach@...gutronix.de; bhelgaas@...gle.com; broonie@...nel.org;
> lorenzo.pieralisi@....com; jingoohan1@...il.com; festevam@...il.com;
> linux-pci@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> linux-kernel@...r.kernel.org; kernel@...gutronix.de; dl-linux-imx
> <linux-imx@....com>
> Subject: Re: [PATCH v8 5/8] PCI: imx6: Refine the regulator usage
> 
> On Mon, Feb 28, 2022 at 03:43:03AM +0000, Hongxing Zhu wrote:
> > > 2. We are playing around with vpcie during regulator during
> > > suspend/resume, why? We currently have issue with suspend/resume
> > > when a PCIe switch is there, with the final effect of PCIe being not
> > > usable afterward. I fear like this is related to our issue.
> > >
> > To my understands, the VPCIE is the abstract of the DIESABLE# signal.
> > Refer to the Chapter 3.1.12.3 W_DISABLE# Signal of PCI Express M.2 SPEC.
> > These signals are used to disable the Adapter's radio operation to
> > meet public Safety regulations or when otherwise desired.
> > It's reasonable to assert/de-assert W_DISABLE# signal during
> suspend/resume.
> >
> > > What about vpcie enable in probe, and vpcie disable in shutdown and
> > > that's all?
> > The W_DISABLE# Signal is used to control the radios on the Adapters.
> > I think you can do that, if the radios are always on in your system.
> 
> According to the binding documentation (imx6q-pcie.yaml)
> 
>   vpcie-supply:
>     description: Should specify the regulator in charge of PCIe port power.
>       The regulator will be enabled when initializing the PCIe host and
>       disabled either as part of the init process or when shutting down
>       the host (optional required).
> 
> This is how it's documented to be used, if this is used according to the
> documentation (and this is happening) what you are already doing (not
> changed in this patch, you are right) is not correct.
> 
> Abusing this for the W_DISABLE# disable is new to me and does not look legit.
The vpcie-supply is one gpio regulator actually, used to control remote Endpoint
 device, through the DISABLE# signal (defined in Mini CEM/M.2 SPEC) of the port.

Best Regards
Richard Zhu

> 
> Francesco