XHCI perform init sequence

kernel/device/xhci.c

@@ -9,6 +9,11 @@
 #include <proc/reschedule.h>
 #include <proc/suspension_q.h>
 #include <sys/debug.h>
+#include <sys/spin_lock.h>
+
+/* REF:
+ * https://www.intel.com/content/dam/www/public/us/en/documents/technical-specifications/extensible-host-controler-interface-usb-xhci.pdf
+ */
 
 /* clang-format off */
 
@@ -97,6 +102,37 @@ DEFINE_DEVICE_INIT (xhci_init) {
   uint32_t dboff = xhci_read32 (xhci->xhci_mmio_base, XHCI_DBOFF);
   xhci->xhci_doorbell_base = xhci->xhci_mmio_base + dboff;
 
+  DEBUG ("starting init sequence\n");
+
+  /* assert CNR is 0 */
+  while (xhci_read32 (xhci->xhci_oper_base, XHCI_USBSTS) & (1 << 11))
+    spin_lock_relax ();
+
+  /* STOP */
+  uint32_t usbcmd = xhci_read32 (xhci->xhci_oper_base, XHCI_USBCMD);
+  xhci_write32 (xhci->xhci_oper_base, XHCI_USBCMD, usbcmd & ~0x01);
+
+  /* wait for HCH bit */
+  int timeout = 100000;
+  while (!(xhci_read32 (xhci->xhci_oper_base, XHCI_USBSTS) & (1 << 12))) {
+    if (--timeout == 0)
+      break;
+
+    spin_lock_relax ();
+  }
+
+  /* RESET */
+  xhci_write32 (xhci->xhci_oper_base, XHCI_USBCMD, (1 << 1));
+
+  while (xhci_read32 (xhci->xhci_oper_base, XHCI_USBCMD) & (1 << 1))
+    spin_lock_relax ();
+
+  /* Stall while controller not ready */
+  while (xhci_read32 (xhci->xhci_oper_base, XHCI_USBSTS) & (1 << 11))
+    spin_lock_relax ();
+
+  DEBUG ("XHCI init done\n");
+
   return true;
 }