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

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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 = {
--
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