From: Alan Stern <stern@rowland.harvard.edu>
To: Mayuresh Kulkarni <mkulkarni@opensource.cirrus.com>
Cc: Oliver Neukum <oneukum@suse.com>,
Greg KH <gregkh@linuxfoundation.org>,
<patches@opensource.cirrus.com>, <linux-usb@vger.kernel.org>
Subject: Re: [PATCH] usb: core: devio: add ioctls for suspend and resume
Date: Thu, 20 Jun 2019 11:49:30 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1906201145280.1512-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <1561043507.20348.26.camel@opensource.cirrus.com>
On Thu, 20 Jun 2019, Mayuresh Kulkarni wrote:
> On Wed, 2019-06-19 at 10:40 -0400, Alan Stern wrote:
> > The only solution I can think of is for the userspace program to first
> > set the device's autosuspend delay to 0. Then whenever the
> > WAIT_FOR_RESUME ioctl returns -- even if it returns immediately -- the
> > program should assume the suspend is over or is not going to happen.
> > Then the program can run normally for a short while (10 seconds,
> > perhaps) before making another attempt to suspend.
> >
>
> Looks like usb_autosuspend_delay parameter is applicable to all USB
> devices. Also, since it is a module parameter, it might be tuned on a
> particular platform (e.g.: from init.<vendor>.rc on Android).
> So, I am not sure if it is good idea to rely on user-space to change it
> and restore it to original value when the USB device of interest is
> detached.
That's up to you. There are lots of different ways to set the
autosuspend delay. For example, you could create a udev rule that
would do it only for the devices your program handles.
> > The only change I would make to the patch posted earlier is to have
> > proc_wait_for_resume() call usb_autoresume_device() and set
> > ps->suspend_requested = false before returning.
> >
> > Mayuresh, how does that sound?
>
> With the code-changes you send me (in response to the
> patch), usb_autoresume_device() will be called when the waiter
> in proc_wait_for_resume() will return and send some message to "know"
> why resume happened.
>
> With above proposed change, proc_wait_for_resume() will return
> with usb_autoresume_device() and suspend_requested = false. So when the
> user-space will send some message to "know" resume reason, the checks in
> ioctl() handler will be skipped.
>
> (Apologies if above is obvious, but still wanted to comment so that we
> are on same page).
>
> With that said, I think there would be an issue with "host-wake" case as
> below - the sequence of operations are:
> - suspend ioctl called: assume actual bus suspend happens
> - wait-for-resume ioctl called
> - after a while user-space wants to send a message (due to end user
> interaction for example)
>
> Here the ioctl() will do usb_autoresume_device() since suspend_requested
> = true. This will end up calling usbfs_notify_resume() which will
> release waiter in proc_wait_for_resume(). And due to above proposed
> change, it will end up calling usb_autoresume_device() again.
>
> As a result, suspend will not happen for next suspend ioctl call.
Obviously the code would need to be more careful. It would call
usb_autoresume_device() only if ps->suspend_requested was true.
Alan Stern
> So, looks like the original proposed change seems better here. On the
> side note, I am still in process of verifying the code changes.
next prev parent reply other threads:[~2019-06-20 15:49 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-10 10:01 [PATCH] usb: core: devio: add ioctls for suspend and resume Mayuresh Kulkarni
2019-06-05 9:41 ` Greg KH
2019-06-05 21:02 ` Alan Stern
2019-06-13 14:00 ` Mayuresh Kulkarni
2019-06-13 20:54 ` Alan Stern
2019-06-17 11:38 ` Mayuresh Kulkarni
2019-06-17 15:55 ` Alan Stern
2019-06-18 14:00 ` Mayuresh Kulkarni
2019-06-18 15:50 ` Alan Stern
2019-06-19 9:19 ` Oliver Neukum
2019-06-19 14:40 ` Alan Stern
2019-06-19 15:12 ` Oliver Neukum
2019-06-19 16:07 ` Alan Stern
2019-06-20 15:11 ` Mayuresh Kulkarni
2019-06-20 15:49 ` Alan Stern [this message]
2019-06-21 16:16 ` Mayuresh Kulkarni
2019-06-21 19:28 ` Alan Stern
2019-06-24 16:02 ` Mayuresh Kulkarni
2019-06-24 17:48 ` Alan Stern
2019-06-25 10:41 ` Mayuresh Kulkarni
2019-06-25 14:08 ` Alan Stern
2019-06-26 7:42 ` Oliver Neukum
2019-06-26 14:35 ` Alan Stern
2019-06-26 14:15 ` Mayuresh Kulkarni
2019-06-26 15:07 ` Alan Stern
2019-06-27 13:20 ` Mayuresh Kulkarni
2019-06-27 13:52 ` Alan Stern
2019-07-01 9:18 ` Oliver Neukum
2019-07-01 14:17 ` Alan Stern
2019-07-02 9:21 ` Oliver Neukum
2019-07-02 14:29 ` Alan Stern
2019-07-03 14:44 ` Mayuresh Kulkarni
2019-07-05 18:51 ` [RFC] usbfs: Add ioctls for runtime " Alan Stern
2019-07-11 9:16 ` Mayuresh Kulkarni
2019-07-11 14:20 ` Alan Stern
2019-07-11 14:36 ` Greg KH
2019-07-25 9:10 ` Mayuresh Kulkarni
2019-07-25 9:18 ` Greg KH
2019-07-25 15:18 ` Alan Stern
2019-07-25 16:05 ` Greg KH
2019-06-20 14:34 ` [PATCH] usb: core: devio: add ioctls for " Mayuresh Kulkarni
2019-06-20 14:43 ` Alan Stern
2019-06-13 13:32 ` Mayuresh Kulkarni
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