linux-kernel - Re: lockdep warning in urb.c:363 usb_submit

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Date:   Sun, 29 Mar 2020 15:56:32 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Qais Yousef <qais.yousef@....com>,
        USB list <linux-usb@...r.kernel.org>,
        Linux-pm mailing list <linux-pm@...r.kernel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: lockdep warning in urb.c:363 usb_submit_urb

On Sun, Mar 29, 2020 at 11:16 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>

[cut]

> >
> > But if SMART_SUSPEND is set and the device is runtime-suspended, why
> > issue the ->suspend callback?
>
> The driver itself or the middle-layer may want to resume the device.
>
> Arguably, it may do that in ->prepare() too,

Not really.

The problem is that that device_prepare() is executed synchronously
for all devices, so if multiple devices needed to be resumed, the
latency would accumulate if that happened in device_prepare().

Cheers!