linux-kernel - [PATCH v2 0/2] Allow DWC3 runtime suspend if UDC is unbinded

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Message-Id: <20201105232825.5233-1-wcheng@codeaurora.org>
Date:   Thu,  5 Nov 2020 15:28:23 -0800
From:   Wesley Cheng <wcheng@...eaurora.org>
To:     balbi@...nel.org, gregkh@...uxfoundation.org,
        stern@...land.harvard.edu, Thinh.Nguyen@...opsys.com
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        jackp@...eaurora.org, Wesley Cheng <wcheng@...eaurora.org>
Subject: [PATCH v2 0/2] Allow DWC3 runtime suspend if UDC is unbinded

Changes in v2:
 - Modified logic for executing the runtime PM resume.  Using a sychronous get
   call to avoid race conditions.

During the following scenario, the DWC3 runtime suspend routine is blocked as
the connected flag is still true:

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

Technically, for device initiated disconnects, there is no active session/link
with the host, so the DWC3 controller should be allowed to go into a low power
state.  Also, we need to now consider when re-binding the UDC,
dwc3_gadget_set_speed() is executed before dwc3_gadget_pullup(), so if the DWC3
controller is suspended/disabled, while accessing the DCFG, that could result in
bus timeouts, etc...  Change the dwc3_gadget_set_speed() to save the speed
being requested, and program it during dwc3_gadget_run_stop(), which is executed
during PM runtime resume.  If not, previous setting will be overridden as we
execute a DWC3 controller reset during PM runtime resume. 

Wesley Cheng (2):
  usb: dwc3: gadget: Allow runtime suspend if UDC unbinded
  usb: dwc3: gadget: Preserve UDC max speed setting

 drivers/usb/dwc3/core.h   |   1 +
 drivers/usb/dwc3/gadget.c | 121 ++++++++++++++++++++++----------------
 2 files changed, 71 insertions(+), 51 deletions(-)

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