linux-kernel - [PATCH V2 1/1] USB: serial: f81232: fix incomplete serial port generation

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Message-ID: <20251128085244.14044-1-peter_hong@fintek.com.tw>
Date: Fri, 28 Nov 2025 16:52:44 +0800
From: "Ji-Ze Hong (Peter Hong)" <peter_hong@...tek.com.tw>
To: <johan@...nel.org>
CC: <gregkh@...uxfoundation.org>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <tom_tsai@...tek.com.tw>,
        <peter_hong@...tek.com.tw>, <yu_chen@...tek.com.tw>
Subject: [PATCH V2 1/1] USB: serial: f81232: fix incomplete serial port generation

The Fintek F81532A/534A/535/536 family relies on the
F81534A_CTRL_CMD_ENABLE_PORT (116h) register during initialization to
both determine serial port status and control port creation. If the
driver experiences fast load/unload cycles, the device state may becomes
unstable, resulting in the incomplete generation of serial ports.

Performing a dummy read operation on the register prior to the initial
write command resolves the issue. This clears the device's stale internal
state. Subsequent write operations will correctly generate all serial
ports.

Tested on: HygonDM1SLT(Hygon C86 3250 8-core Processor)

Signed-off-by: Ji-Ze Hong (Peter Hong) <peter_hong@...tek.com.tw>
---
Changelog:
v2:
	1. remove loop in accessor function.

 drivers/usb/serial/f81232.c | 38 +++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/drivers/usb/serial/f81232.c b/drivers/usb/serial/f81232.c
index 530b77fc2f78..c587c58cbacf 100644
--- a/drivers/usb/serial/f81232.c
+++ b/drivers/usb/serial/f81232.c
@@ -856,6 +856,21 @@ static int f81534a_ctrl_set_register(struct usb_interface *intf, u16 reg,
 	return status;
 }
 
+static int f81534a_ctrl_get_register(struct usb_interface *intf, u16 reg,
+					u16 size, void *val)
+{
+	return usb_control_msg_recv(interface_to_usbdev(intf),
+						0,
+						F81232_REGISTER_REQUEST,
+						F81232_GET_REGISTER,
+						reg,
+						0,
+						val,
+						size,
+						USB_CTRL_GET_TIMEOUT,
+						GFP_KERNEL);
+}
+
 static int f81534a_ctrl_enable_all_ports(struct usb_interface *intf, bool en)
 {
 	unsigned char enable[2] = {0};
@@ -869,6 +884,29 @@ static int f81534a_ctrl_enable_all_ports(struct usb_interface *intf, bool en)
 	 * bit 0~11	: Serial port enable bit.
 	 */
 	if (en) {
+		/*
+		 * The Fintek F81532A/534A/535/536 family relies on the
+		 * F81534A_CTRL_CMD_ENABLE_PORT (116h) register during
+		 * initialization to both determine serial port status and
+		 * control port creation.
+		 *
+		 * If the driver experiences fast load/unload cycles, the
+		 * device state may becomes unstable, resulting in the
+		 * incomplete generation of serial ports.
+		 *
+		 * Performing a dummy read operation on the register prior
+		 * to the initial write command resolves the issue.
+		 *
+		 * This clears the device's stale internal state. Subsequent
+		 * write operations will correctly generate all serial ports.
+		 */
+		status = f81534a_ctrl_get_register(intf,
+						F81534A_CTRL_CMD_ENABLE_PORT,
+						sizeof(enable),
+						enable);
+		if (status)
+			return status;
+
 		enable[0] = 0xff;
 		enable[1] = 0x8f;
 	}
-- 
2.34.1