Re: [PATCH v13 10/15] PCI: imx6: Turn off regulator when system is in suspend mode

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Jun 28, 2022 at 03:48:01AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@kernel.org>
> > Sent: 2022年6月28日 3:52
> > To: Hongxing Zhu <hongxing.zhu@nxp.com>
> > Cc: l.stach@pengutronix.de; bhelgaas@google.com; robh+dt@kernel.org;
> > broonie@kernel.org; lorenzo.pieralisi@arm.com; festevam@gmail.com;
> > francesco.dolcini@toradex.com; linux-pci@vger.kernel.org;
> > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> > kernel@pengutronix.de; dl-linux-imx <linux-imx@nxp.com>
> > Subject: Re: [PATCH v13 10/15] PCI: imx6: Turn off regulator when system is in
> > suspend mode
> > 
> > On Fri, Jun 24, 2022 at 05:05:00AM +0000, Hongxing Zhu wrote:
> > > > -----Original Message-----
> > > > From: Bjorn Helgaas <helgaas@kernel.org>
> > > > Sent: 2022年6月24日 6:20
> > > > To: Hongxing Zhu <hongxing.zhu@nxp.com>
> > > > Cc: l.stach@pengutronix.de; bhelgaas@google.com; robh+dt@kernel.org;
> > > > broonie@kernel.org; lorenzo.pieralisi@arm.com; festevam@gmail.com;
> > > > francesco.dolcini@toradex.com; linux-pci@vger.kernel.org;
> > > > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> > > > kernel@pengutronix.de; dl-linux-imx <linux-imx@nxp.com>
> > > > Subject: Re: [PATCH v13 10/15] PCI: imx6: Turn off regulator when
> > > > system is in suspend mode
> > > >
> > > > On Fri, Jun 17, 2022 at 06:31:09PM +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().
> > > > >
> > > > > Move the regulator_disable to the suspend function, turn off
> > > > > regulator when the system is in suspend mode.
> > > > >
> > > > > To keep the balance of the regulator usage counter, disable the
> > > > > regulator in shutdown.
> > > > >
> > > > > Link:
> > > > > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2F
> > > > > lore
> > > > > .kernel.org%2Fr%2F1655189942-12678-6-git-send-email-hongxing.z&am
> > p
> > > > > ;d
> > > > at
> > > > >
> > > >
> > a=05%7C01%7Chongxing.zhu%40nxp.com%7C5633fa1bf3c443e203e108da55
> > > > 667dc2%
> > > > >
> > > >
> > 7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C6379161959277276
> > > > 04%7CUnkn
> > > > >
> > > >
> > own%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1
> > > > haWwi
> > > > >
> > > >
> > LCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=1Kbzn3XSVvt3gGPrEy%2
> > > > BET8EZn4I
> > > > > dwS%2BhUZ3AalZ2YZ0%3D&amp;reserved=0
> > > > > hu@nxp.com
> > > > > Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
> > > > > Signed-off-by: Bjorn Helgaas <bhelgaas@google.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 2b42c37f1617..f72eb609769b 100644
> > > > > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > > > > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > > > > @@ -670,8 +670,6 @@ static void imx6_pcie_clk_disable(struct
> > > > > imx6_pcie
> > > > > *imx6_pcie)
> > > > >
> > > > >  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:
> > > > > @@ -702,14 +700,6 @@ static void
> > > > > imx6_pcie_assert_core_reset(struct
> > > > imx6_pcie *imx6_pcie)
> > > > >  		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);
> > > > > -	}
> > > > > -
> > > > >  	/* Some boards don't have PCIe reset GPIO. */
> > > > >  	if (gpio_is_valid(imx6_pcie->reset_gpio))
> > > > >  		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> > > > > @@ -722,7 +712,7 @@ static int
> > > > > imx6_pcie_deassert_core_reset(struct
> > > > imx6_pcie *imx6_pcie)
> > > > >  	struct device *dev = pci->dev;
> > > > >  	int ret;
> > > > >
> > > > > -	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", @@
> > > > -795,7
> > > > > +785,7 @@ 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", @@
> > > > -1022,6
> > > > > +1012,9 @@ static int imx6_pcie_suspend_noirq(struct device *dev)
> > > > >  		break;
> > > > >  	}
> > > > >
> > > > > +	if (imx6_pcie->vpcie)
> > > > > +		regulator_disable(imx6_pcie->vpcie);
> > > > > +
> > > > >  	return 0;
> > > > >  }
> > > >
> > > > The suspend and resume methods should be symmetric, and they should
> > > > *look* symmetric.
> > > >
> > > > imx6_pcie_suspend_noirq() disables the regulator, so
> > > > imx6_pcie_resume_noirq() should enable it.
> > > >
> > > > imx6_pcie_suspend_noirq() calls imx6_pcie_clk_disable() to disable
> > > > several clocks.  imx6_pcie_resume_noirq() should call
> > > > imx6_pcie_clk_enable() to enable them.
> > > >
> > > > imx6_pcie_clk_enable() *is* called in the resume path, but it's
> > > > buried inside imx6_pcie_host_init() and
> > > > imx6_pcie_deassert_core_reset().  That makes it hard to analyze.
> > > >
> > > > We should be able to look at imx6_pcie_suspend_noirq() and
> > > > imx6_pcie_resume_noirq() and easily see that the resume path resumes
> > > > everything that was suspended in the suspend path.
> > >
> > > Yes, it is. It's better to keep suspend/resume symmetric as much as
> > > possible.  In resume, the host_init is invoked, clocks, regulators and
> > > so on would be initialized properly.
> > >
> > > Unfortunately, there is no according host_exit() that can be called to
> > > do the reversed clocks, regulators disable operations in the suspend.
> > > So, the clocks and regulator disable are explicitly invoked in suspend
> > > callback.
> > >
> > > How about to do the incremental updates if the .host_exit can be added
> > > later?
> > 
> > This doesn't seem very convincing because everything here is in the
> > imx6 domain.  The only DWC core thing here is the dw_pcie_setup_rc() called
> > in imx6_pcie_resume_noirq(), and it doesn't call back to any
> > imx6 code.
> > 
> > So you should be able to make an imx6_pcie_host_exit() or whatever that
> > corresponds to imx6_pcie_host_init().
>
> Thanks for your kindly help to review it. That's reasonable.
> 
> So, to make it symmetric with imx6_pcie_host_init() and
> imx6_pcie_start_link().  The according local functions
> imx6_pcie_host_exit() and imx6_pcie_stop_link() would be created.
> 
> BTW, to be symmetric with imx6_pcie_host_init(), the parameter of
> imx6_pcie_host_exit() is same to the parameter of
> imx6_pcie_host_init().  So do imx6_pcie_stop_link() and
> imx6_pcie_start_link().  Are you satisfied with the following
> functions?
> 
> static void imx6_pcie_stop_link(struct dw_pcie *pci)
> {
>         struct device *dev = pci->dev;
> 
>         /* Turn off PCIe LTSSM */
>         imx6_pcie_ltssm_disable(dev);
> }
> 
> static void imx6_pcie_host_exit(struct pcie_port *pp)
> {
>         struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>         struct imx6_pcie *imx6_pcie = to_imx6_pcie(pci);
> 
>         imx6_pcie_clk_disable(imx6_pcie);
>         if (imx6_pcie->phy) {
>                 if (phy_power_off(imx6_pcie->phy))
>                         dev_err(pci->dev, "unable to power off PHY\n");
>                 phy_exit(imx6_pcie->phy);
>         }
> 
>         if (imx6_pcie->vpcie)
>                 regulator_disable(imx6_pcie->vpcie);
> }

After the current series, imx6_pcie_host_init() looks like:

  imx6_pcie_host_init
    phy_power_on
    regulator_enable
    imx6_pcie_deassert_core_reset
      imx6_pcie_clk_enable
    phy_init

and you propose:

  imx6_pcie_host_exit
    imx6_pcie_clk_disable
    phy_power_off
    phy_exit
    regulator_disable

Generally they should do things in the reverse order.

imx6_pcie_host_init() does phy_power_on(), regulator_enable(),
imx6_pcie_clk_enable().

imx6_pcie_host_exit() should do imx6_pcie_clk_disable(),
regulator_disable(), phy_power_off().

(It looks like imx6_pcie_host_init() calls phy_power_on() and
phy_init() in the wrong order [1].)

IMO the imx6_pcie_clk_enable() should not be hidden inside
imx6_pcie_deassert_core_reset().

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/phy/phy-core.c?id=v5.19-rc1#n233

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