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

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Message-ID: <AS8PR04MB8676418087498F9CAF9849FD8C019@AS8PR04MB8676.eurprd04.prod.outlook.com>
Date:   Mon, 28 Feb 2022 03:43:03 +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2月25日 17:43
> To: Hongxing Zhu <hongxing.zhu@....com>
> Cc: l.stach@...gutronix.de; bhelgaas@...gle.com; broonie@...nel.org;
> lorenzo.pieralisi@....com; jingoohan1@...il.com; festevam@...il.com;
> francesco.dolcini@...adex.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 Fri, Feb 25, 2022 at 11:44:24AM +0800, Richard Zhu wrote:
> > The driver should undo any enables it did itself. The regulator
> > disable shouldn't be basing decisions on regulator_is_enabled().
> >
> > To keep the balance of the regulator usage counter, disable the
> > regulator just behind of imx6_pcie_assert_core_reset() in resume and
> shutdown.
> 
> While this patch does not look wrong and improving the existing code, I do
> have a couple of concern.
> 
> 1. It's weird that regulator enable/disable are really non symmetric in the code,
> enable is in imx6_pcie_deassert_core_reset(), while disable is not in
> imx6_pcie_assert_core_reset() but spread around.
Hi Francesco:
This regulator disable was a part of imx6_pcie_assert_core_reset() before,
 just had been moved out of imx6_pcie_assert_core_reset() in this refine
 commit.

> 
> 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.

Best Regards
Richard
> 
> Francesco
> 
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c | 19 +++++++------------
> >  1 file changed, 7 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 0f1b8c873a4a..160a0bd02098 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -369,8 +369,6 @@ static int imx6_pcie_attach_pd(struct device *dev)
> >
> >  static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
> > {
> > -	struct device *dev = imx6_pcie->pci->dev;
> > -
> >  	switch (imx6_pcie->drvdata->variant) {
> >  	case IMX7D:
> >  	case IMX8MQ:
> > @@ -400,14 +398,6 @@ static void imx6_pcie_assert_core_reset(struct
> imx6_pcie *imx6_pcie)
> >  				   IMX6Q_GPR1_PCIE_REF_CLK_EN, 0 << 16);
> >  		break;
> >  	}
> > -
> > -	if (imx6_pcie->vpcie && regulator_is_enabled(imx6_pcie->vpcie) > 0) {
> > -		int ret = regulator_disable(imx6_pcie->vpcie);
> > -
> > -		if (ret)
> > -			dev_err(dev, "failed to disable vpcie regulator: %d\n",
> > -				ret);
> > -	}
> >  }
> >
> >  static unsigned int imx6_pcie_grp_offset(const struct imx6_pcie
> > *imx6_pcie) @@ -584,7 +574,7 @@ static int
> imx6_pcie_deassert_core_reset(struct imx6_pcie *imx6_pcie)
> >  	struct device *dev = pci->dev;
> >  	int ret, err;
> >
> > -	if (imx6_pcie->vpcie && !regulator_is_enabled(imx6_pcie->vpcie)) {
> > +	if (imx6_pcie->vpcie) {
> >  		ret = regulator_enable(imx6_pcie->vpcie);
> >  		if (ret) {
> >  			dev_err(dev, "failed to enable vpcie regulator: %d\n", @@
> -657,7
> > +647,7 @@ static int imx6_pcie_deassert_core_reset(struct imx6_pcie
> *imx6_pcie)
> >  	return 0;
> >
> >  err_clks:
> > -	if (imx6_pcie->vpcie && regulator_is_enabled(imx6_pcie->vpcie) > 0) {
> > +	if (imx6_pcie->vpcie) {
> >  		ret = regulator_disable(imx6_pcie->vpcie);
> >  		if (ret)
> >  			dev_err(dev, "failed to disable vpcie regulator: %d\n", @@
> -1029,6
> > +1019,9 @@ static int imx6_pcie_resume_noirq(struct device *dev)
> >  		return 0;
> >
> >  	imx6_pcie_assert_core_reset(imx6_pcie);
> > +	if (imx6_pcie->vpcie)
> > +		regulator_disable(imx6_pcie->vpcie);
> > +
> >  	imx6_pcie_init_phy(imx6_pcie);
> >  	imx6_pcie_deassert_core_reset(imx6_pcie);
> >  	dw_pcie_setup_rc(pp);
> > @@ -1262,6 +1255,8 @@ static void imx6_pcie_shutdown(struct
> > platform_device *pdev)
> >
> >  	/* bring down link, so bootloader gets clean state in case of reboot */
> >  	imx6_pcie_assert_core_reset(imx6_pcie);
> > +	if (imx6_pcie->vpcie)
> > +		regulator_disable(imx6_pcie->vpcie);
> >  }
> >
> >  static const struct imx6_pcie_drvdata drvdata[] = {
> > --
> > 2.25.1
> >