linux-kernel - Re: [RFC PATCH v2] USB: hub: fix port suspend/resume

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Message-ID: <Pine.LNX.4.44L0.2002271100000.1730-100000@iolanthe.rowland.org>
Date:   Thu, 27 Feb 2020 11:18:41 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Marco Felsch <m.felsch@...gutronix.de>
cc:     gregkh@...uxfoundation.org, <Thinh.Nguyen@...opsys.com>,
        <harry.pan@...el.com>, <nobuta.keiya@...itsu.com>,
        <malat@...ian.org>, <kai.heng.feng@...onical.com>,
        <chiasheng.lee@...el.com>, <andreyknvl@...gle.com>,
        <heinzelmann.david@...il.com>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <kernel@...gutronix.de>,
        kbuild test robot <lkp@...el.com>
Subject: Re: [RFC PATCH v2] USB: hub: fix port suspend/resume

On Thu, 27 Feb 2020, Marco Felsch wrote:

> At the momemnt the usb-port driver has only runime_pm hooks.
> Suspending the port and turn off the VBUS supply should be triggered by
> the hub device suspend callback usb_port_suspend() which calls the

Strictly speaking it's just a routine, not a callback.  That is, it 
doesn't get invoked through a function pointer.

> pm_runtime_put_sync() if all pre-conditions are meet. This mechanism
> don't work correctly due to the global PM behaviour, for more information
> see [1]. According [1] I added the suspend/resume callbacks for the port
> device to fix this.
> 
> [1] https://www.spinics.net/lists/linux-usb/msg190537.html

Please put at least a short description of the problem here; don't 
force people to go look up some random web page just to find out what's 
really going on.

> Signed-off-by: Marco Felsch <m.felsch@...gutronix.de>
> ---
> Hi,
> 
> this v2 contains the fixes
> 
> Reported-by: kbuild test robot <lkp@...el.com>

Everything below the "---" line, except the patch itself, gets ignored.  
You need to move this Reported-by: up higher.

> Regards,
>   Marco
> 
> Changes:
> - init retval to zero
> - keep CONFIG_PM due to do_remote_wakeup availability
> - adapt commit message
> 
>  drivers/usb/core/hub.c  | 13 -------------
>  drivers/usb/core/port.c | 35 ++++++++++++++++++++++++++++++-----
>  2 files changed, 30 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 3405b146edc9..c294484e478d 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -3323,10 +3323,6 @@ int usb_port_suspend(struct usb_device *udev, pm_message_t msg)
>  		usb_set_device_state(udev, USB_STATE_SUSPENDED);
>  	}
>  
> -	if (status == 0 && !udev->do_remote_wakeup && udev->persist_enabled
> -			&& test_and_clear_bit(port1, hub->child_usage_bits))
> -		pm_runtime_put_sync(&port_dev->dev);
> -
>  	usb_mark_last_busy(hub->hdev);
>  
>  	usb_unlock_port(port_dev);
> @@ -3514,15 +3510,6 @@ int usb_port_resume(struct usb_device *udev, pm_message_t msg)
>  	int		status;
>  	u16		portchange, portstatus;
>  
> -	if (!test_and_set_bit(port1, hub->child_usage_bits)) {
> -		status = pm_runtime_get_sync(&port_dev->dev);
> -		if (status < 0) {
> -			dev_dbg(&udev->dev, "can't resume usb port, status %d\n",
> -					status);
> -			return status;
> -		}
> -	}
> -

Why do you get rid of these two sections of code?  Won't that cause
runtime PM to stop working properly?

>  	usb_lock_port(port_dev);
>  
>  	/* Skip the initial Clear-Suspend step for a remote wakeup */
> diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
> index bbbb35fa639f..13f130b67efe 100644
> --- a/drivers/usb/core/port.c
> +++ b/drivers/usb/core/port.c
> @@ -283,7 +283,34 @@ static int usb_port_runtime_suspend(struct device *dev)
>  
>  	return retval;
>  }
> -#endif
> +
> +static int __maybe_unused _usb_port_suspend(struct device *dev)

Don't say _maybe_unused.  Instead, protect these two routines with 
#ifdef CONFIG_PM_SLEEP.  That way they won't be compiled on systems 
that can't use them.

Also, try to find better names.  Maybe usb_port_sleep and 
usb_port_wake, or usb_port_system_suspend and usb_port_system_resume.

> +{
> +	struct usb_port *port_dev = to_usb_port(dev);
> +	struct usb_device *udev = port_dev->child;
> +	int retval = 0;
> +
> +	if (!udev->do_remote_wakeup && udev->persist_enabled)
> +		retval = usb_port_runtime_suspend(dev);
> +
> +	/* Do not force the user to enable the power-off feature */
> +	if (retval && retval != -EAGAIN)
> +		return retval;
> +
> +	return 0;

IMO it would be a lot more understandable if you wrote

	if (retval == -EAGAIN)
		retval = 0;

Also, the relation between this code and the preceding comment is not
obvious.  The comment should say something more like: If the
PM_QOS_FLAG setting prevents us from powering off the port, it's not an
error.

Alan Stern

> +}
> +
> +static int __maybe_unused _usb_port_resume(struct device *dev)
> +{
> +	struct usb_port *port_dev = to_usb_port(dev);
> +	struct usb_device *udev = port_dev->child;
> +
> +	if (!udev->do_remote_wakeup && udev->persist_enabled)
> +		return usb_port_runtime_resume(dev);
> +
> +	return 0;
> +}
> +#endif /* CONFIG_PM */
>  
>  static void usb_port_shutdown(struct device *dev)
>  {
> @@ -294,10 +321,8 @@ static void usb_port_shutdown(struct device *dev)
>  }
>  
>  static const struct dev_pm_ops usb_port_pm_ops = {
> -#ifdef CONFIG_PM
> -	.runtime_suspend =	usb_port_runtime_suspend,
> -	.runtime_resume =	usb_port_runtime_resume,
> -#endif
> +	SET_SYSTEM_SLEEP_PM_OPS(_usb_port_suspend, _usb_port_resume)
> +	SET_RUNTIME_PM_OPS(usb_port_runtime_suspend, usb_port_runtime_resume, NULL)
>  };
>  
>  struct device_type usb_port_device_type = {
>