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From: Frank Li <Frank.Li@nxp.com>
To: ran.wang_1@nxp.com,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
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	linux-usb@vger.kernel.org (open list:USB SUBSYSTEM),
	devicetree@vger.kernel.org (open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS),
	linux-kernel@vger.kernel.org (open list)
Cc: devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-usb@vger.kernel.org,
	mark.rutland@arm.com,
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	sergei.shtylyov@cogentembedded.com
Subject: [PATCH 1/2] dt-bindings: usb: dwc3: Add snps,host-vbus-glitches avoiding vbus glitch
Date: Fri, 19 Jan 2024 16:31:28 -0500
Message-Id: <20240119213130.3147517-1-Frank.Li@nxp.com>
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From: Ran Wang <ran.wang_1@nxp.com>

When DWC3 is set to host mode by programming register DWC3_GCTL, VBUS
(or its control signal) will turn on immediately on related Root Hub
ports. Then the VBUS will be de-asserted for a little while during xhci
reset (conducted by xhci driver) for a little while and back to normal.

This VBUS glitch might cause some USB devices emuration fail if kernel
boot with them connected. One SW workaround which can fix this is to
program all PORTSC[PP] to 0 to turn off VBUS immediately after setting
host mode in DWC3 driver(per signal measurement result, it will be too
late to do it in xhci-plat.c or xhci.c).

Signed-off-by: Ran Wang <ran.wang_1@nxp.com>
Reviewed-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
 Documentation/devicetree/bindings/usb/snps,dwc3.yaml | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
index 203a1eb66691f..dbf272b76e0b5 100644
--- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
+++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
@@ -273,6 +273,13 @@ properties:
       with an external supply.
     type: boolean
 
+  snps,host-vbus-glitches:
+    description:
+      When set, power off all Root Hub ports immediately after
+      setting host mode to avoid vbus (negative) glitch happen in later
+      xhci reset. And the vbus will back to 5V automatically when reset done.
+    type: boolean
+
   snps,is-utmi-l1-suspend:
     description:
       True when DWC3 asserts output signal utmi_l1_suspend_n, false when
-- 
2.34.1