[RFC PATCH 1/2] dt-bindings: usb: snps,dwc3: Add 'snps,gadget-keep-connect-sys-sleep'

[Roger Quadros <rogerq@kernel.org>]

The current USB gadget driver behaviour is to stop the controller
and disconnect from the bus during System sleep.

The 'snps,gadget-keep-connect-sys-sleep' property can be used to
change this behaviour and keep the controller active and connected
to the bus during System sleep. This is useful for applications
that want to enter a low power state when USB is suspended but
remain connected so they can resume activity on USB resume.

This feature introduces a new constraint if Gadget driver is connected
to USB host: i.e.  the gadget must be in USB suspend state to allow
a System sleep as we cannot process any USB transactions
when in System sleep.

The system hardware is responsible to detect the end of USB suspend
and wake up the system so we can begin processing the USB transactions
as soon as possible.

Cc: devicetree@vger.kernel.org
Signed-off-by: Roger Quadros <rogerq@kernel.org>
---
 Documentation/devicetree/bindings/usb/snps,dwc3.yaml | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
index be36956af53b..1ce8008e7fef 100644
--- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
+++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
@@ -262,6 +262,11 @@ properties:
       asserts utmi_sleep_n.
     type: boolean
 
+  snps,gadget-keep-connect-sys-sleep:
+    description:
+      If True then gadget driver will not disconnect during system sleep.
+      System sleep will not be allowed if gadget is not already in USB suspend.
+
   snps,hird-threshold:
     description: HIRD threshold
     $ref: /schemas/types.yaml#/definitions/uint8
-- 
2.34.1