mpfs_usb: Add mpfs_vbus_detect

External function to query vbus status. Reading from the block requires
the clock, but if no devices are open -> vbus detect does not work.

This creates a chicken / egg problem, if vbus detect is used to start
the usb device.

arch/risc-v/src/mpfs/mpfs_usb.c

@@ -228,6 +228,7 @@ static void   mpfs_epset_reset(struct mpfs_usbdev_s *priv, uint16_t epset);
  ****************************************************************************/
 
 static struct mpfs_usbdev_s g_usbd;
+static uint8_t g_clkrefs;
 
 static const struct usbdev_epops_s g_epops =
 {
@@ -433,7 +434,18 @@ static inline void mpfs_putreg8(uint8_t regval, uintptr_t regaddr)
 
 static void mpfs_enableclk(void)
 {
-  modifyreg32(MPFS_SYSREG_SUBBLK_CLOCK_CR, 0, SYSREG_SUBBLK_CLOCK_CR_USB);
+  /* Handle the counter atomically */
+
+  irqstate_t flags = enter_critical_section();
+
+  if (g_clkrefs == 0)
+    {
+      modifyreg32(MPFS_SYSREG_SUBBLK_CLOCK_CR, 0,
+                  SYSREG_SUBBLK_CLOCK_CR_USB);
+    }
+
+  g_clkrefs++;
+  leave_critical_section(flags);
 }
 
 /****************************************************************************
@@ -452,7 +464,18 @@ static void mpfs_enableclk(void)
 
 static void mpfs_disableclk(void)
 {
-  modifyreg32(MPFS_SYSREG_SUBBLK_CLOCK_CR, SYSREG_SUBBLK_CLOCK_CR_USB, 0);
+  /* Handle the counter atomically */
+
+  irqstate_t flags = enter_critical_section();
+
+  g_clkrefs--;
+  if (g_clkrefs == 0)
+    {
+      modifyreg32(MPFS_SYSREG_SUBBLK_CLOCK_CR, SYSREG_SUBBLK_CLOCK_CR_USB,
+                  0);
+    }
+
+  leave_critical_section(flags);
 }
 
 /****************************************************************************
@@ -4001,3 +4024,29 @@ errout:
   mpfs_usbuninitialize();
 }
 
+/****************************************************************************
+ * Name: mpfs_vbus_detect
+ *
+ * Description:
+ *   Read the VBUS state from the USB OTG controller.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   true if VBUS is valid; false otherwise
+ *
+ ****************************************************************************/
+
+bool mpfs_vbus_detect(void)
+{
+  uint8_t vbus;
+
+  /* Accessing the peripheral needs the clock */
+
+  mpfs_enableclk();
+  vbus = getreg8(MPFS_USB_DEV_CTRL) & DEV_CTRL_VBUS_MASK;
+  mpfs_disableclk();
+
+  return vbus == VBUS_ABOVE_VBUS_VALID;
+}

arch/risc-v/src/mpfs/mpfs_usb.h

@@ -63,6 +63,22 @@ extern "C"
 
 void mpfs_usbinitialize(void);
 
+/****************************************************************************
+ * Name: mpfs_vbus_detect
+ *
+ * Description:
+ *   Read the VBUS state from the USB OTG controller.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   true if VBUS is valid; false otherwise
+ *
+ ****************************************************************************/
+
+bool mpfs_vbus_detect(void);
+
 #undef EXTERN
 #if defined(__cplusplus)
 }