[PATCH 2/2] serial: Poll USB devices if usbX serial port is missing

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

If usbX serial port is missing, try to poll USB devices. This makes them
appear at least on Intel NUC devices DN2820FYKH and DCCP847DYE.

This fixes cases where you try to configure usbX serial at the beginning
of a script, like:

  serial usb0 --speed=115200 --word=8 --parity=none --stop=1
  terminal_output --append serial_usb0
  terminal_input --append serial_usb0

Without this patch the above would fail with:

  serial port `usb0' isn't found

Strangely, adding 'usb' command before the serial initialization
made it work, and even moving the terminal_output and input command
to be before. This is due to the terminal_output command detecting
"serial_usb" and running USB polling if the output is missing. 'usb'
command from usbtest module always polls USB devices.

As it is the logical thing to configure the serial port before adding
it as an output or input, this patch makes things works as expected.
Most online resources mentioning GRUB and USB serial adapters also do
mention the above order, so there must be quite many struggling with
this problem on platforms where USB needs to be polled in order for
the detection to happen.

Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
 grub-core/term/serial.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/grub-core/term/serial.c b/grub-core/term/serial.c
index db80b3b..1f856a2 100644
--- a/grub-core/term/serial.c
+++ b/grub-core/term/serial.c
@@ -191,6 +191,7 @@ grub_cmd_serial (grub_extcmd_context_t ctxt, int argc, char **args)
   struct grub_serial_port *port;
   struct grub_serial_config config;
   grub_err_t err;
+  int again;
 
   if (state[OPTION_UNIT].set)
     {
@@ -212,7 +213,25 @@ grub_cmd_serial (grub_extcmd_context_t ctxt, int argc, char **args)
   if (!name)
     name = "com0";
 
-  port = grub_serial_find (name);
+  again = 0;
+  while(1)
+    {
+      port = grub_serial_find (name);
+
+      if (port || again)
+	break;
+
+      if (grub_memcmp (name, "usb", sizeof ("usb") - 1) == 0)
+	{
+	  grub_usb_poll_devices(1);
+	  again = 1;
+	}
+      else
+	{
+	  break;
+	}
+    }
+
   if (!port)
     return grub_error (GRUB_ERR_BAD_ARGUMENT, 
 		       N_("serial port `%s' isn't found"),
-- 
2.7.4