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From: Wesley Cheng <wcheng@codeaurora.org>
To: Linux USB List <linux-usb@vger.kernel.org>
Subject: dwc3: Power management for cable disconnect
Date: Fri, 16 Oct 2020 00:29:19 -0700	[thread overview]
Message-ID: <0fe1cf51-c9d4-9780-e542-a613bba58928@codeaurora.org> (raw)

Hi linux-usb members!

I was looking at seeing how the DWC3 drivers are handling the USB cable
disconnect routine (VBUS low situation) when there is no UDC binded.  Is
the below behavior expected?

1.  Enumerate device w/ host.
2.  Gadget is unbinded
	- echo "" > /sys/kernel/config/usb_gadget/g1/UDC
3.  Disconnect the USB cable (VBUS low)
4.  No dwc3_gadget_disconnect_interrupt() seen (since controller is
   halted from step#1)
5.  Runtime PM autosuspend fails due to "dwc->connected" being true
(cleared in dwc3_gadget_disconnect_interrupt())
6.  Gadget binded
	- echo udc_name > /sys/kernel/config/usb_gadget/g1/UDC
7.  No runtime suspend until cable is plugged in and out

This would be problematic for devices which have to reliably enter
suspend.  I just wanted to see if this is a scenario which has been
considered?  Seems odd that we would still keep the controller out of
low power if there was no cable connected.

Thanks

Regards,
Wesley Cheng

-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

             reply	other threads:[~2020-10-16  7:29 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-16  7:29 Wesley Cheng [this message]
2020-10-16 22:42 ` dwc3: Power management for cable disconnect Thinh Nguyen
2020-10-20  5:46   ` Wesley Cheng

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