xen: support console_switching between Dom0 and DomUs on ARM

Today Ctrl-AAA is used to switch between Xen and Dom0. Extend the
mechanism to allow for switching between Xen, Dom0, and any of the
initial DomU created from Xen alongside Dom0 out of information provided
via device tree.

Rename xen_rx to console_rx to match the new behavior.

Clarify existing comment about "notify the guest", making it clear that
it is only about the hardware domain.

Switching the console input to domUs started from Xen at boot is
#ifdef'ed to 0 in this patch. The code will be enabled when
vpl011_rx_char_xen is introduced. For now it is disabled for
bisectability.

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
CC: andrew.cooper3@citrix.com
CC: George.Dunlap@eu.citrix.com
CC: ian.jackson@eu.citrix.com
CC: jbeulich@suse.com
CC: konrad.wilk@oracle.com
CC: tim@xen.org
CC: wei.liu2@citrix.com

xen/drivers/char/console.c

@@ -31,10 +31,13 @@
 #include <xen/early_printk.h>
 #include <xen/warning.h>
 #include <xen/pv_console.h>
+#include <asm/setup.h>
 
 #ifdef CONFIG_X86
 #include <xen/consoled.h>
 #include <asm/guest.h>
+#else
+#include <asm/vpl011.h>
 #endif
 
 /* console: comma-separated list of console outputs. */
@@ -391,31 +394,82 @@ static void dump_console_ring_key(unsigned char key)
     free_xenheap_pages(buf, order);
 }
 
-/* CTRL-<switch_char> switches input direction between Xen and DOM0. */
+/*
+ * CTRL-<switch_char> changes input direction, rotating among Xen, Dom0,
+ * and the DomUs started from Xen at boot.
+ */
 #define switch_code (opt_conswitch[0]-'a'+1)
-static int __read_mostly xen_rx = 1; /* FALSE => input passed to domain 0. */
+/*
+ * console_rx=0 => input to xen
+ * console_rx=1 => input to dom0
+ * console_rx=N => input to dom(N-1)
+ */
+static unsigned int __read_mostly console_rx = 0;
 
 static void switch_serial_input(void)
 {
-    static char *input_str[2] = { "DOM0", "Xen" };
-    xen_rx = !xen_rx;
-    printk("*** Serial input -> %s", input_str[xen_rx]);
+    if ( console_rx == max_init_domid + 1 )
+    {
+        console_rx = 0;
+        printk("*** Serial input to Xen");
+    }
+    else
+    {
+        console_rx++;
+        printk("*** Serial input to DOM%d", console_rx - 1);
+    }
+
     if ( switch_code )
-        printk(" (type 'CTRL-%c' three times to switch input to %s)",
-               opt_conswitch[0], input_str[!xen_rx]);
+        printk(" (type 'CTRL-%c' three times to switch input)",
+               opt_conswitch[0]);
     printk("\n");
 }
 
 static void __serial_rx(char c, struct cpu_user_regs *regs)
 {
-    if ( xen_rx )
+    switch ( console_rx )
+    {
+    case 0:
         return handle_keypress(c, regs);
 
-    /* Deliver input to guest buffer, unless it is already full. */
-    if ( (serial_rx_prod-serial_rx_cons) != SERIAL_RX_SIZE )
-        serial_rx_ring[SERIAL_RX_MASK(serial_rx_prod++)] = c;
-    /* Always notify the guest: prevents receive path from getting stuck. */
-    send_global_virq(VIRQ_CONSOLE);
+    case 1:
+        /*
+         * Deliver input to the hardware domain buffer, unless it is
+         * already full.
+         */
+        if ( (serial_rx_prod - serial_rx_cons) != SERIAL_RX_SIZE )
+            serial_rx_ring[SERIAL_RX_MASK(serial_rx_prod++)] = c;
+
+        /*
+         * Always notify the hardware domain: prevents receive path from
+         * getting stuck.
+         */
+        send_global_virq(VIRQ_CONSOLE);
+        break;
+
+#if 0
+    default:
+    {
+        struct domain *d = rcu_lock_domain_by_any_id(console_rx - 1);
+
+        /*
+         * If we have a properly initialized vpl011 console for the
+         * domain, without a full PV ring to Dom0 (in that case input
+         * comes from the PV ring), then send the character to it.
+         */
+        if ( d != NULL &&
+             !d->arch.vpl011.backend_in_domain &&
+             d->arch.vpl011.backend.xen != NULL )
+            vpl011_rx_char_xen(d, c);
+        else
+            printk("Cannot send chars to Dom%d: no UART available\n",
+                   console_rx - 1);
+
+        if ( d != NULL )
+            rcu_unlock_domain(d);
+    }
+#endif
+    }
 
 #ifdef CONFIG_X86
     if ( pv_shim && pv_console )
@@ -944,7 +998,7 @@ void __init console_endboot(void)
      * a useful 'how to switch' message.
      */
     if ( opt_conswitch[1] == 'x' )
-        xen_rx = !xen_rx;
+        console_rx = max_init_domid + 1;
 
     register_keyhandler('w', dump_console_ring_key,
                         "synchronously dump console ring buffer (dmesg)", 0);