From: Mayuresh Kulkarni <mkulkarni@opensource.cirrus.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: <linux-usb@vger.kernel.org>
Subject: Re: About usb_new_device() API
Date: Mon, 5 Aug 2019 09:43:14 +0100 [thread overview]
Message-ID: <1564994594.2877.12.camel@opensource.cirrus.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1908021221120.1645-100000@iolanthe.rowland.org>
On Fri, 2019-08-02 at 12:27 -0400, Alan Stern wrote:
> On Fri, 2 Aug 2019, Mayuresh Kulkarni wrote:
>
> >
> > Hi Alan,
> >
> > Thanks a lot for clearing out the confusion.
> >
> > Our USB device can operate in 2 mutually exclusive modes: one is
> > normal
> > composite USB audio mode and other is vendor specific HID device
> > mode.
> >
> > On the same platform (Android based):
> > - When the device is in normal composite USB audio mode,
> > "cat /sys/bus/usb/devices/.../power/control" show "auto".
> > - When the device is in vendor specific HID device mode,
> > "cat /sys/bus/usb/devices/.../power/control" show "on".
> >
> > And hence as per your comment, I am unable to see USB-2.0 L2 for
> > vendor
> > specific HID device mode.
> >
> > I guess I need to find out "who" is setting the /power/control =
> > "auto"
> > when composite USB audio device is detected. And explore if it could
> > be
> > moved to a more generic place.
> I'm pretty sure this is done by some program, not automatically done
> by
> the kernel.
I think I found what is happening here:
- Looks like, the USB audio class driver is
calling usb_enable_autosuspend().
- Please check $KERNEL_SRC/sound/usb, card.c, usb_audio_probe().
- It is using interface_to_usbdev() to get the parent of its interface
device, which is the USB device allocated by the hub driver.
And hence, in above use-case, I can see L2 when our device is in
composite USB-audio mode.
Moreover, the HID-class driver doesn't seem to call
usb_enable_autosuspend() on its parent and hence I don't see L2 when our
device operates as a vendor specific HID device.
So a simple fix would be to call usb_enable_autosuspend() from HID class
driver as well.
With that said, what would be your recommendation here, Alan -
1. Is it OK for USB-class drivers to call usb_enable_autosuspend() on
their parent device to ensure low power state is entered?
OR
2. Is it recommended to call usb_enable_autosuspend() from user-space by
writing "auto" to "cat /sys/bus/usb/devices/.../power/control"?
In my opinion, both should be fine.
Thanks,
>
> >
> > Is there any module parameter (or some other means) by which,
> > power/control (or deprecated power/level) will always be "auto", by
> > default?
> No, there isn't. The power/control (or power/level) attribute has to
> be set by the user or a program.
>
> Alan Stern
>
next prev parent reply other threads:[~2019-08-05 8:43 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 14:49 About usb_new_device() API Mayuresh Kulkarni
2019-08-01 17:51 ` Alan Stern
2019-08-02 15:43 ` Mayuresh Kulkarni
2019-08-02 16:27 ` Alan Stern
2019-08-05 8:43 ` Mayuresh Kulkarni [this message]
2019-08-05 14:07 ` Alan Stern
2019-08-05 16:30 ` Mayuresh Kulkarni
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1564994594.2877.12.camel@opensource.cirrus.com \
--to=mkulkarni@opensource.cirrus.com \
--cc=linux-usb@vger.kernel.org \
--cc=stern@rowland.harvard.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).