kvm,serial: Enable THRI bit in IIR register

This patch enables the THRI ("transmission holding register empty") bit in the
IIR register to make sure the guest doesn't think we have data waiting for it.

Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --git a/tools/kvm/early_printk.c b/tools/kvm/early_printk.c
index a10d35846309cbf665973630666c984abe2b20e1..d5db3a12a523b8693a4e9ff09f4e5807d9c12e51 100644 (file)
--- a/tools/kvm/early_printk.c
+++ b/tools/kvm/early_printk.c
@@ -24,6 +24,7 @@
 #define IIR            2
 
 #define UART_IIR_NO_INT                0x01
+#define UART_IIR_THRI          0x02
 
 /* 16550 FIFO Control Register */
 #define FCR            2
@@ -130,13 +131,13 @@ static bool serial8250_in(struct kvm *self, uint16_t port, void *data, int size,
 
        switch (offset) {
        case THR:
-               ioport__write8(data, 0x00);
+               /* TODO: input support */
                break;
        case IER:
                ioport__write8(data, device.ier);
                break;
        case IIR:
-               ioport__write8(data, UART_IIR_NO_INT);
+               ioport__write8(data, UART_IIR_NO_INT | UART_IIR_THRI);
                break;
        case LCR:
                ioport__write8(data, device.lcr);