linux-kernel - RE: [PATCH v1] PCI: imx6: Keep the GPIO regulator always on

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Message-ID: <AS8PR04MB8676B8B896C3A4F2F4BAF6D28C389@AS8PR04MB8676.eurprd04.prod.outlook.com>
Date:   Thu, 3 Nov 2022 08:05:27 +0000
From:   Hongxing Zhu <hongxing.zhu@....com>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>
CC:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v1] PCI: imx6: Keep the GPIO regulator always on

Hi Ahmad
Thanks for your review comments.

> -----Original Message-----
> From: Ahmad Fatoum <a.fatoum@...gutronix.de>
> Sent: 2022年11月3日 15:05
> To: Hongxing Zhu <hongxing.zhu@....com>; l.stach@...gutronix.de;
> bhelgaas@...gle.com; lorenzo.pieralisi@....com
> Cc: linux-pci@...r.kernel.org; linux-kernel@...r.kernel.org; dl-linux-imx
> <linux-imx@....com>; kernel@...gutronix.de;
> linux-arm-kernel@...ts.infradead.org
> Subject: Re: [PATCH v1] PCI: imx6: Keep the GPIO regulator always on
> 
> Hello Richard,
> 
> On 03.11.22 07:08, Richard Zhu wrote:
> > Since vpcie regulator is one GPIO regulator, used to control the
> > VPCIe_3V3 and power up remote PCIe EP device.
> 
> Regulator need not be a GPIO regulator. I'd drop this from the title.
> 
Got that, thanks.

> > Some WIFI modules load their firmware once in probe, and can't be
> > powered off during suspend. Otherwise, these WIFI modules wouldn't be
> > functional anymore after resume back.
> 
> The brcmfmac OTOH, reprobes when resuming from suspend. Before this patch,
> AFAIU, it should've been possible for the EP to go into D3cold during suspend.
> This may no longer be possible when we keep vpcie powered.
> 
Oh, understood. In the other words, the EP wouldn't be in D3 mode when vpcie
 is always powered on, right?
Thanks for your detailed explains.

> > So, keep this regulator always on in the probe.
> >
> > Fixes: a4bb720eeb1e ("PCI: imx6: Turn off regulator when system is in
> > suspend mode")
> 
> Prior to a4bb720eeb1e, vpcie was briefly toggled during PCIe core reset
> sequence, so aforementioned WiFi modules that don't reprobe over resume
> should've been broken by that too? If so, I don't see how it fixes that commit
> as everything that is broken now was broken before that commit as well. After
> this patch however, modules that can accept vpcie being toggled can't benefit
> from some of the power saving.
The WIFI modules that don't re-probe over resume are always broken, if the
 vpcie is toggled during suspend/resume, I think.

BTW, is the re-probe over resume mandatory requirements for EP devices
(for example, WIFI modules)?
I'm curious that how the WIFI remote wake up going on if the WIFI module
 is totally powered off.

> 
> Why can't users with this issue use a regulator-always-on regulator instead?
Yes, you're right.
One regulator-always-on regulator is a good idea.

> 
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c | 24 ++++++++----------------
> >  1 file changed, 8 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 2616585ca5f8..94a89bbf381d 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -926,22 +926,13 @@ static int imx6_pcie_host_init(struct dw_pcie_rp
> *pp)
> >  	struct imx6_pcie *imx6_pcie = to_imx6_pcie(pci);
> >  	int ret;
> >
> > -	if (imx6_pcie->vpcie) {
> > -		ret = regulator_enable(imx6_pcie->vpcie);
> > -		if (ret) {
> > -			dev_err(dev, "failed to enable vpcie regulator: %d\n",
> > -				ret);
> > -			return ret;
> > -		}
> > -	}
> > -
> >  	imx6_pcie_assert_core_reset(imx6_pcie);
> >  	imx6_pcie_init_phy(imx6_pcie);
> >
> >  	ret = imx6_pcie_clk_enable(imx6_pcie);
> >  	if (ret) {
> >  		dev_err(dev, "unable to enable pcie clocks: %d\n", ret);
> > -		goto err_reg_disable;
> > +		return ret;
> >  	}
> >
> >  	if (imx6_pcie->phy) {
> > @@ -974,9 +965,6 @@ static int imx6_pcie_host_init(struct dw_pcie_rp
> *pp)
> >  		phy_exit(imx6_pcie->phy);
> >  err_clk_disable:
> >  	imx6_pcie_clk_disable(imx6_pcie);
> > -err_reg_disable:
> > -	if (imx6_pcie->vpcie)
> > -		regulator_disable(imx6_pcie->vpcie);
> >  	return ret;
> >  }
> >
> > @@ -991,9 +979,6 @@ static void imx6_pcie_host_exit(struct dw_pcie_rp
> *pp)
> >  		phy_exit(imx6_pcie->phy);
> >  	}
> >  	imx6_pcie_clk_disable(imx6_pcie);
> > -
> > -	if (imx6_pcie->vpcie)
> > -		regulator_disable(imx6_pcie->vpcie);
> >  }
> >
> >  static const struct dw_pcie_host_ops imx6_pcie_host_ops = { @@
> > -1263,6 +1248,13 @@ static int imx6_pcie_probe(struct platform_device
> *pdev)
> >  		if (PTR_ERR(imx6_pcie->vpcie) != -ENODEV)
> >  			return PTR_ERR(imx6_pcie->vpcie);
> >  		imx6_pcie->vpcie = NULL;
> > +	} else {
> > +		ret = regulator_enable(imx6_pcie->vpcie);
> > +		if (ret) {
> > +			dev_err(dev, "failed to enable vpcie regulator: %d\n",
> > +				ret);
> > +			return ret;
> > +		}
> 
> Shouldn't the regulator enable be undone if the probe later fails?
> 
Yes, it's required.
Thanks a lot for your comments.

Richard Zhu
Best Regards
> Cheers,
> Ahmad
> 
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