linux-kernel - Re: [PATCH v2 1/2] USB: core: Disable remote wakeup for freeze/quiesce

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Message-ID: <Yl7KEX++hJac8T6I@rowland.harvard.edu>
Date:   Tue, 19 Apr 2022 10:41:21 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Evan Green <evgreen@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Rajat Jain <rajatja@...omium.org>,
        Razvan Heghedus <heghedus.razvan@...il.com>,
        Wei Ming Chen <jj251510319013@...il.com>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 1/2] USB: core: Disable remote wakeup for
 freeze/quiesce

On Mon, Apr 18, 2022 at 02:00:45PM -0700, Evan Green wrote:
> The PM_EVENT_FREEZE and PM_EVENT_QUIESCE messages should cause the
> device to stop generating interrupts. USB core was previously allowing
> devices that were already runtime suspended to keep remote wakeup
> enabled if they had gone down that way. This violates the contract with
> pm, and can potentially cause MSI interrupts to be lost.
> 
> Change that so that if a device is runtime suspended with remote wakeups
> enabled, it will be resumed to ensure remote wakeup is always disabled
> across a freeze.
> 
> Signed-off-by: Evan Green <evgreen@...omium.org>
> ---
> 
> (no changes since v1)
> 
>  drivers/usb/core/driver.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index 355ed33a21792b..93c8cf66adccec 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -1533,20 +1533,18 @@ static void choose_wakeup(struct usb_device *udev, pm_message_t msg)
>  {
>  	int	w;
>  
> -	/* Remote wakeup is needed only when we actually go to sleep.
> -	 * For things like FREEZE and QUIESCE, if the device is already
> -	 * autosuspended then its current wakeup setting is okay.
> +	/* For FREEZE/QUIESCE, disable remote wakeups so no interrupts get generated
> +	 * by the device.

You mean "by the host controller".  USB devices don't generate 
interrupts; they generate wakeup requests (which can cause a host 
controller to generate an interrupt).

>  	 */
>  	if (msg.event == PM_EVENT_FREEZE || msg.event == PM_EVENT_QUIESCE) {
> -		if (udev->state != USB_STATE_SUSPENDED)
> -			udev->do_remote_wakeup = 0;
> -		return;
> -	}
> +		w = 0;
>  
> -	/* Enable remote wakeup if it is allowed, even if no interface drivers
> -	 * actually want it.
> -	 */
> -	w = device_may_wakeup(&udev->dev);
> +	} else {
> +		/* Enable remote wakeup if it is allowed, even if no interface drivers
> +		 * actually want it.
> +		 */
> +		w = device_may_wakeup(&udev->dev);
> +	}
>  
>  	/* If the device is autosuspended with the wrong wakeup setting,
>  	 * autoresume now so the setting can be changed.
> -- 

I would prefer it if you reformatted the comments to agree with the 
current style:

	/*
	 * Blah blah blah
	 */

and to avoid line wrap beyond 80 columns.  Apart from that:

Acked-by: Alan Stern <stern@...land.harvard.edu>

Alan Stern