netdev - Re: [PATCH 4/7] usbnet: cdc_mbim: don't recover device if suspend fails in system sleep

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Date:	Tue, 05 Mar 2013 16:03:21 +0100
From:	Bjørn Mork <bjorn@...k.no>
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>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH 4/7] usbnet: cdc_mbim: don't recover device if suspend fails in system sleep

Ming Lei <ming.lei@...onical.com> writes:
> On Tue, Mar 5, 2013 at 9:46 PM, Bjørn Mork <bjorn@...k.no> wrote:
>
>> Now, after inspecting wdm_suspend() which hides behind
>> info->subdriver->suspend(), I see that this is a completely theoretical
>> discussion as it always will return 0 if PMSG_IS_AUTO(msg) is true...
>>
>> Which means that your change really is a noop().  I still don't like it,
>> because it gives the impression that errors from info->subdriver->suspend()
>> isn't dealt with.
>
> Yes, it needn't dealt with in system sleep, so it has the document benefit.

The document that the return code is ignored by forcing it to 0 and
always return success.

But am still not convinced this is correct in any way.  AFAICS there is
no documentation stating that the drivers should care about what the USB
core use the return value for. Drivers are allowed to fail and the core
will ignore and clean up if necessary.

I still find any partial failures horrendous.  If we are not going to
fail on errors, then we'll return success and pretend to be suspended.

> No, USB core does not handle it, and will always ignore the return
> failure from driver's suspend, see usb_suspend_both() for non-autosuspend
> case.

Right you are.  Somehow I read the inverse.  Sorry about that.

In any case, it ends up here and everythin will be OK, which I assume is
why it can ignore the errors:

        /* If the suspend succeeded then prevent any more URB submissions
         * and flush any outstanding URBs.
         */
        } else {
                udev->can_submit = 0;
                for (i = 0; i < 16; ++i) {
                        usb_hcd_flush_endpoint(udev, udev->ep_out[i]);
                        usb_hcd_flush_endpoint(udev, udev->ep_in[i]);
                }
        }


Bjørn
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