[PATCH 1/2] phy: rockchip: inno-usb2: fix disconnection in gadget mode

[Luca Ceresoli]

From: Louis Chauvet <louis.chauvet at bootlin.com>

When the OTG USB port is used to power to SoC, configured as peripheral and
used in gadget mode, there is a disconnection about 6 seconds after the
gadget is configured and enumerated.

The problem was observed on a Radxa Rock Pi S board, which can only be
powered by the only USB-C connector. That connector is the only one usable
in gadget mode. This implies the USB cable is connected from before boot
and never disconnects while the kernel runs.

The problem happens because of the PHY driver code flow, summarized as:

 * UDC start code (triggered via configfs at any time after boot)
   -> phy_init
       -> rockchip_usb2phy_init
           -> schedule_delayed_work(otg_sm_work [A], 6 sec)
   -> phy_power_on
       -> rockchip_usb2phy_power_on
           -> enable clock
           -> rockchip_usb2phy_reset

 * Now the gadget interface is up and running.

 * 6 seconds later otg_sm_work starts [A]
   -> rockchip_usb2phy_otg_sm_work():
       if (B_IDLE state && VBUS present && ...):
           schedule_delayed_work(&rport->chg_work [B], 0);

 * immediately the chg_detect_work starts [B]
   -> rockchip_chg_detect_work():
       if chg_state is UNDEFINED:
           if (!rport->suspended):
               rockchip_usb2phy_power_off() <--- [X]

At [X], the PHY is powered off, causing a disconnection. This quickly
triggers a new connection and following re-enumeration, but any connection
that had been established during the 6 seconds is broken.

The code already checks for !rport->suspended, so add a guard for VBUS as
well to avoid a disconnection when a cable is connected.

Fixes: 98898f3bc83c ("phy: rockchip-inno-usb2: support otg-port for rk3399")
Closes: https://lore.kernel.org/lkml/20250414185458.7767aabc@booty/
Co-developed-by: Luca Ceresoli <luca.ceresoli at bootlin.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>
Signed-off-by: Louis Chauvet <louis.chauvet at bootlin.com>
---
 drivers/phy/rockchip/phy-rockchip-inno-usb2.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/phy/rockchip/phy-rockchip-inno-usb2.c b/drivers/phy/rockchip/phy-rockchip-inno-usb2.c
index b0f23690ec3002202c0f33a6988f5509622fa10e..0106d7b7ae24ead91d9c996daaa56671de02a39a 100644
--- a/drivers/phy/rockchip/phy-rockchip-inno-usb2.c
+++ b/drivers/phy/rockchip/phy-rockchip-inno-usb2.c
@@ -821,14 +821,16 @@ static void rockchip_chg_detect_work(struct work_struct *work)
 		container_of(work, struct rockchip_usb2phy_port, chg_work.work);
 	struct rockchip_usb2phy *rphy = dev_get_drvdata(rport->phy->dev.parent);
 	struct regmap *base = get_reg_base(rphy);
-	bool is_dcd, tmout, vout;
+	bool is_dcd, tmout, vout, vbus_attach;
 	unsigned long delay;
 
+	vbus_attach = property_enabled(rphy->grf, &rport->port_cfg->utmi_bvalid);
+
 	dev_dbg(&rport->phy->dev, "chg detection work state = %d\n",
 		rphy->chg_state);
 	switch (rphy->chg_state) {
 	case USB_CHG_STATE_UNDEFINED:
-		if (!rport->suspended)
+		if (!rport->suspended && !vbus_attach)
 			rockchip_usb2phy_power_off(rport->phy);
 		/* put the controller in non-driving mode */
 		property_enable(base, &rphy->phy_cfg->chg_det.opmode, false);

-- 
2.50.1