From: Alan Stern <stern@rowland.harvard.edu>
To: Mayuresh Kulkarni <mkulkarni@opensource.cirrus.com>
Cc: linux-usb@vger.kernel.org
Subject: Re: About usb_new_device() API
Date: Fri, 2 Aug 2019 12:27:26 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1908021221120.1645-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <1564760625.15747.9.camel@opensource.cirrus.com>
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.
> 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:[~2019-08-02 16:27 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 [this message]
2019-08-05 8:43 ` Mayuresh Kulkarni
2019-08-05 14:07 ` Alan Stern
2019-08-05 16:30 ` Mayuresh Kulkarni
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