netdev - Re: [PATCH v2 1/7] USB: adds comment on suspend callback

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Date:	Thu, 7 Mar 2013 15:26:02 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <ming.lei@...onical.com>
cc:	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Oliver Neukum <oneukum@...e.de>,
	<netdev@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	<linux-input@...r.kernel.org>
Subject: Re: [PATCH v2 1/7] USB: adds comment on suspend callback

On Fri, 8 Mar 2013, Ming Lei wrote:

> This patch adds comments on interface driver suspend callback
> to emphasize that the failure return value is ignored by
> USB core in system sleep context, so do not try to recover
> device for this case and let resume/reset_resume callback
> handle the suspend failure if needed.
> 
> Also kerneldoc for usb_suspend_both() is updated with the
> fact.
> 
> Signed-off-by: Ming Lei <ming.lei@...onical.com>
> ---
>  drivers/usb/core/driver.c |   11 ++++++++---
>  include/linux/usb.h       |    7 ++++++-
>  2 files changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index d938b2b..eb1d00a 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -1196,9 +1196,14 @@ done:
>   *
>   * This is the central routine for suspending USB devices.  It calls the
>   * suspend methods for all the interface drivers in @udev and then calls
> - * the suspend method for @udev itself.  If an error occurs at any stage,
> - * all the interfaces which were suspended are resumed so that they remain
> - * in the same state as the device.
> + * the suspend method for @udev itself.  When the routine is called in
> + * autosuspend, if an error occurs at any stage, all the interfaces
> + * which were suspended are resumed so that they remain in the same
> + * state as the device, but when called from system sleep, all error
> + * from suspend methods of interfaces and the non-root-hub device itself
> + * are simply ignored, so all suspended interfaces are only resumed
> + * to the device's state when @udev is root-hub and its suspend method
> + * returns failure.
>   *
>   * Autosuspend requests originating from a child device or an interface
>   * driver may be made without the protection of @udev's device lock, but
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index 4d22d0f..f82ce57 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -978,7 +978,12 @@ struct usbdrv_wrap {
>   *	the "usbfs" filesystem.  This lets devices provide ways to
>   *	expose information to user space regardless of where they
>   *	do (or don't) show up otherwise in the filesystem.
> - * @suspend: Called when the device is going to be suspended by the system.
> + * @suspend: Called when the device is going to be suspended by the
> + *	system either from system sleep or runtime suspend context. The
> + *	return value will be ignored in system sleep context, so do NOT
> + *	try to continue using the device if suspend fails in this case.
> + *	Instead, let the resume or reset-resume routine recover from
> + *	the failure.
>   * @resume: Called when the device is being resumed by the system.
>   * @reset_resume: Called when the suspended device has been reset instead
>   *	of being resumed.

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

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