linux-kernel - Re: [PATCH v1 2/2] usb: core: enable remote wakeup function for usb controller

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Date:   Wed, 8 Dec 2021 17:04:57 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     Yinbo Zhu <zhuyinbo@...ngson.cn>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Rajat Jain <rajatja@...gle.com>,
        Chris Chiu <chris.chiu@...onical.com>,
        linux-usb@...r.kernel.org, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] usb: core: enable remote wakeup function for usb
 controller

On Wed, Dec 08, 2021 at 05:39:51PM +0800, Yinbo Zhu wrote:
> The remote wake up function is a regular function on usb device and
> I think keeping it enabled by default will make the usb application
> more convenient and usb device remote wake up function keep enabled
> that ask usb controller remote wake up was enabled at first.
> 
> This patch only enable wake up on usb root hub device, among which,

You say the patch only affects root hub devices, but this doesn't appear 
to be true.

> usb3.0 root hub doesn't be set wakeup node property but use command
> USB_INTRF_FUNC_SUSPEND to enable remote wake up function.
> 
> Signed-off-by: Yinbo Zhu <zhuyinbo@...ngson.cn>
> ---
>  drivers/usb/core/hub.c | 20 ++++++++++++++++++--
>  include/linux/usb.h    |  4 +++-
>  2 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 86658a8..cb4b956 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2509,6 +2509,8 @@ static void set_usb_port_removable(struct usb_device *udev)
>   */
>  int usb_new_device(struct usb_device *udev)
>  {
> +	struct usb_host_config *config;
> +	int ncfg;
>  	int err;
>  
>  	if (udev->parent) {
> @@ -2540,6 +2542,18 @@ int usb_new_device(struct usb_device *udev)
>  	udev->dev.devt = MKDEV(USB_DEVICE_MAJOR,
>  			(((udev->bus->busnum-1) * 128) + (udev->devnum-1)));
>  
> +	for (ncfg = 0; ncfg < udev->descriptor.bNumConfigurations; ncfg++) {
> +		config = &udev->config[ncfg];
> +		if ((config->desc.bmAttributes & (1 << 5)) == 0)
> +			break;
> +		if (ncfg + 1 == udev->descriptor.bNumConfigurations) {
> +			err = usb_enable_remote_wakeup(udev);
> +			if (err)
> +				dev_dbg(&udev->dev,
> +				      "won't remote wakeup, err %d\n", err);
> +		}
> +	}

I don't see anything in there which treats root hubs differently from 
other devices.

Besides, enabling wakeup for root hubs is generally a bad idea.  Suppose 
you closed a laptop's lid and then unplugged a USB device -- with wakeup 
enabled, the unplug would cause the laptop to wake up again without your 
knowledge.

Alan Stern