linux-kernel - [PATCH 7/9] usb: misc: qcom_eud: fix virtual attach/detach event handling

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Message-Id: <20260116232106.2234978-8-elson.serrao@oss.qualcomm.com>
Date: Fri, 16 Jan 2026 15:21:04 -0800
From: Elson Serrao <elson.serrao@....qualcomm.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Souradeep Chowdhury <quic_schowdhu@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 7/9] usb: misc: qcom_eud: fix virtual attach/detach event handling

EUD provides virtual USB attach/detach events to simulate cable
plug/unplug while maintaining the physical debug connection. However,
the current implementation incorrectly sets the USB role to HOST on
virtual detach, which doesn't represent the disconnected state.

Fix the virtual detach handling by setting the USB role to NONE
instead of HOST, correctly representing the disconnected state.

Signed-off-by: Elson Serrao <elson.serrao@....qualcomm.com>
---
 drivers/usb/misc/qcom_eud.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/misc/qcom_eud.c b/drivers/usb/misc/qcom_eud.c
index 3f1cc7ea2a6a..60f566427abe 100644
--- a/drivers/usb/misc/qcom_eud.c
+++ b/drivers/usb/misc/qcom_eud.c
@@ -343,10 +343,26 @@ static irqreturn_t handle_eud_irq_thread(int irq, void *data)
 	if (!path || !path->controller_sw)
 		goto clear_irq;
 
+	/*
+	 * EUD virtual attach/detach event handling for low power debugging:
+	 *
+	 * When EUD is enabled in debug mode, the device remains physically
+	 * connected to the PC throughout the debug session, keeping the USB
+	 * controller active. This prevents testing of low power scenarios that
+	 * require USB disconnection.
+	 *
+	 * EUD solves this by providing virtual USB attach/detach events while
+	 * maintaining the physical connection. These events are triggered from
+	 * the Host PC via the enumerated EUD control interface and delivered
+	 * to the EUD driver as interrupts.
+	 *
+	 * These notifications are forwarded to the USB controller through role
+	 * switch framework.
+	 */
 	if (chip->usb_attached)
 		ret = usb_role_switch_set_role(path->controller_sw, USB_ROLE_DEVICE);
 	else
-		ret = usb_role_switch_set_role(path->controller_sw, USB_ROLE_HOST);
+		ret = usb_role_switch_set_role(path->controller_sw, USB_ROLE_NONE);
 	if (ret)
 		dev_err(chip->dev, "failed to set role switch\n");
 
-- 
2.34.1