drivers: usb: dc: stm32: fix usb_disable() deadlock on certain series

During a teardown sequence performed by the USB DC stack's "usb_disable()",
the controller is first disabled by calling "usb_dc_detach()", which turns
off the USB controller clock in the STM32 implementation. "usb_disable()"
then disables endpoints by calling "usb_dc_ep_disable()" on each of them,
which is merely forwarded to HAL_PCD_EP_Close() by the STM32 driver. This
order of operations means that the latter operation is actually operating
on the no-longer-clocks USB controller! Up until recently, memory accesses
to MMIO of unclocked peripherals in STM32 SoCs would not cause issues, even
if the resulting access was a no-op (read returns zero, write is ignored),
so everything worked fine even if the access was *technically* illegal...
However, on newer series with a different bus fabric, accesses to unclocked
peripherals will instead deadlock the SoC!

Prevent illegal accesses inside "usb_dc_stm32_ep_disable()" by checking if
the USB controller clock is enabled before calling HAL_PCD_EP_Close(), and
skipping the call if it isn't. This allows "usb_disable()" to complete on
series such as STM32N6.

Signed-off-by: Mathieu Choplain <[email protected]>

Author: mathieuchopstm

drivers/usb/device/usb_dc_stm32.c

@@ -201,6 +201,16 @@ static struct usb_dc_stm32_state usb_dc_stm32_state;
 
 /* Internal functions */
 
+static bool usb_dc_stm32_clock_enabled(void)
+{
+	const struct device *const clk = DEVICE_DT_GET(STM32_CLOCK_CONTROL_NODE);
+
+	enum clock_control_status status = clock_control_get_status(
+						clk, (clock_control_subsys_t)&pclken[0]);
+
+	return status == CLOCK_CONTROL_STATUS_ON;
+}
+
 static struct usb_dc_stm32_ep_state *usb_dc_stm32_get_ep_state(uint8_t ep)
 {
 	struct usb_dc_stm32_ep_state *ep_state_base;
@@ -940,6 +950,17 @@ int usb_dc_ep_disable(const uint8_t ep)
 		return -EINVAL;
 	}
 
+	if (!usb_dc_stm32_clock_enabled()) {
+		/*
+		 * During device teardown, EP disable is attempted after
+		 * the USB controller clock has been turned off. Accessing
+		 * it would do nothing and even deadlocks the SoC on certain
+		 * series: don't even bother trying. Return success as all
+		 * endpoints are disabled anyways when USB controller is off.
+		 */
+		return 0;
+	}
+
 	status = HAL_PCD_EP_Close(&usb_dc_stm32_state.pcd, ep);
 	if (status != HAL_OK) {
 		LOG_ERR("HAL_PCD_EP_Close failed(0x%02x), %d", ep,