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

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Message-ID: <3bf26670-6af5-e580-76cc-304c759befaf@collabora.com>
Date:   Wed, 24 Aug 2016 16:48:01 -0400
From:   Robert Foss <robert.foss@...labora.com>
To:     Brian Norris <briannorris@...omium.org>
Cc:     mathias.nyman@...el.com, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Julius Werner <jwerner@...omium.org>,
        Andrew Bresticker <abrestic@...omium.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Baolin Wang <baolin.wang@...aro.org>, zyx@...k-chips.com,
        wulf@...k-chips.com
Subject: Re: [PACTH,v6,1/2] usb: xhci: plat: Enable runtime PM



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@...labora.com wrote:
>> From: Robert Foss <robert.foss@...labora.com>
>>
>> Enable runtime PM for the xhci-plat device so that the parent device
>> may implement runtime PM.
>>
>> Signed-off-by: Robert Foss <robert.foss@...labora.com>
>>
>> Tested-by: Robert Foss <robert.foss@...labora.com>
>> ---
>>  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 = {