uart: add resume method and enable it for attachments on the most common

x86 buses

Otherwise the uart hardware could be in such a state after the resume
where IER is cleared and thus no interrupts are generated.

This behavior is observed and tested with QEMU, so I am comitting this
change to help with my debugging.
There has been no feedback from users of serial ports on real hardware.

MFC after:	20 days

1 files changed, 9 insertions, 0 deletions

diff --git a/sys/dev/uart/uart_core.c b/sys/dev/uart/uart_core.c
index 47d5f3d..f5a9a1c 100644
--- a/sys/dev/uart/uart_core.c
+++ b/sys/dev/uart/uart_core.c
@@ -590,3 +590,12 @@ uart_bus_detach(device_t dev)
 
 	return (0);
 }
+
+int
+uart_bus_resume(device_t dev)
+{
+	struct uart_softc *sc;
+
+	sc = device_get_softc(dev);
+	return (UART_ATTACH(sc));
+}