Re: [PACTH,v6,1/2] usb: xhci: plat: Enable runtime PM

[Robert Foss]

On 2016-08-22 11:23 PM, Brian Norris wrote:
> + others
>
> Hi Robert and Felipe,
>
> I have a few questions for one or both of you. I'm not really an expert
> on runtime PM, so please take my questions with a grain of salt.
>
> On Wed, Aug 10, 2016 at 04:32:15PM -0400, robert.foss@xxxxxxxxxxxxx wrote:
> > From: Robert Foss <robert.foss@xxxxxxxxxxxxx>
> >
> > Enable runtime PM for the xhci-plat device so that the parent device
> > may implement runtime PM.
> >
> > Signed-off-by: Robert Foss <robert.foss@xxxxxxxxxxxxx>
> >
> > Tested-by: Robert Foss <robert.foss@xxxxxxxxxxxxx>
> > ---
> >  drivers/usb/host/xhci-plat.c | 29 +++++++++++++++++++++++++++--
> >  1 file changed, 27 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> > index ed56bf9..ba4efe7 100644
> > --- a/drivers/usb/host/xhci-plat.c
> > +++ b/drivers/usb/host/xhci-plat.c
> > @@ -246,6 +246,9 @@ static int xhci_plat_probe(struct platform_device *pdev)
> >  	if (ret)
> >  		goto dealloc_usb2_hcd;
> >
> > +	pm_runtime_set_active(&pdev->dev);
> > +	pm_runtime_enable(&pdev->dev);
> > +
>
> How does it help to enable PM runtime like this, if you don't have any
> kind of runtime_{suspend,resume}() callbacks?

Andrew, I think you understand the inner workings of this code better 
than me, maybe you could give a short summary?

> I suspect that this patch set was derived from the Chromium OS kernel
> tree, where we were supporting a Tegra XHCI chipset:
>
> https://chromium.googlesource.com/chromiumos/third_party/kernel/+/chromeos-3.10/drivers/usb/host/xhci-tegra.c#1920
>
> It looks like the driver was refactored to not use xhci-plat.c before it
> was upstreamed (and runtime PM support was dropped along the way).
>
> So, I'm wondering how I might actually use this? Particularly, I'm
> looking at trying out runtime suspend for a DWC3 controller in host
> mode, and it looks like I'd have to do some layer-violating calls to
> xhci_suspend()/xhci_resume() from the parent dwc3 device, or else
> rewrite drivers/usb/dwc3/host.c to avoid using xhci-plat.c.
>
> (I also see that Baolin, CC'd here, was interested in dwc3 [1].)
>
> Or possibly an enlightening question for me: if you don't mind, how are
> you utilizing runtime PM in conjunction with xhci-plat.c, Robert?
> Presumably some other parent device/driver is doing some additional
> management of the XHCI core?
>
> Regards,
> Brian
>
> [1] [PATCH 4/4] usb: dwc3: core: Support the dwc3 host suspend/resume
>     https://lkml.org/lkml/2016/7/15/181
>     https://patchwork.kernel.org/patch/9231417/
>
> >  	return 0;
> >
> >
> > @@ -274,6 +277,8 @@ static int xhci_plat_remove(struct platform_device *dev)
> >  	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
> >  	struct clk *clk = xhci->clk;
> >
> > +	pm_runtime_disable(&dev->dev);
> > +
> >  	usb_remove_hcd(xhci->shared_hcd);
> >  	usb_phy_shutdown(hcd->usb_phy);
> >
> > @@ -292,6 +297,13 @@ static int xhci_plat_suspend(struct device *dev)
> >  {
> >  	struct usb_hcd	*hcd = dev_get_drvdata(dev);
> >  	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
> > +	int ret;
> > +
> > +	ret = pm_runtime_get_sync(dev);
> > +	if (ret < 0) {
> > +		pm_runtime_put(dev);
> > +		return ret;
> > +	}
> >
> >  	/*
> >  	 * xhci_suspend() needs `do_wakeup` to know whether host is allowed
> > @@ -301,15 +313,28 @@ static int xhci_plat_suspend(struct device *dev)
> >  	 * reconsider this when xhci_plat_suspend enlarges its scope, e.g.,
> >  	 * also applies to runtime suspend.
> >  	 */
> > -	return xhci_suspend(xhci, device_may_wakeup(dev));
> > +	ret = xhci_suspend(xhci, device_may_wakeup(dev));
> > +	pm_runtime_put(dev);
> > +
> > +	return ret;
> >  }
> >
> >  static int xhci_plat_resume(struct device *dev)
> >  {
> >  	struct usb_hcd	*hcd = dev_get_drvdata(dev);
> >  	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
> > +	int ret;
> >
> > -	return xhci_resume(xhci, 0);
> > +	ret = pm_runtime_get_sync(dev);
> > +	if (ret < 0) {
> > +		pm_runtime_put(dev);
> > +		return ret;
> > +	}
> > +
> > +	ret = xhci_resume(xhci, 0);
> > +	pm_runtime_put(dev);
> > +
> > +	return ret;
> >  }
> >
> >  static const struct dev_pm_ops xhci_plat_pm_ops = {