[PATCH v7 05/16] emul/ns16x50: implement SCR register

[dmukhin@xxxxxxx]

From: Denis Mukhin <dmukhin@xxxxxxxx> 

Add SCR register emulation to the I/O port handler.
Firmware (e.g. OVMF) may use SCR during the guest OS boot.

Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes since v6:
- default handling of non-DLL/DLM registers moved to the previous patch
---
 xen/common/emul/vuart/ns16x50.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/xen/common/emul/vuart/ns16x50.c b/xen/common/emul/vuart/ns16x50.c
index da8583a1dc93..5643ef4cc01e 100644
--- a/xen/common/emul/vuart/ns16x50.c
+++ b/xen/common/emul/vuart/ns16x50.c
@@ -106,6 +106,11 @@ static int ns16x50_io_write8(
     {
         switch ( reg )
         {
+        /* NB: Firmware (e.g. OVMF) may rely on SCR presence. */
+        case UART_SCR:
+            regs[UART_SCR] = val;
+            break;
+
         default:
             rc = -EINVAL;
             break;
@@ -177,6 +182,10 @@ static int ns16x50_io_read8(
     {
         switch ( reg )
         {
+        case UART_SCR:
+            val = regs[UART_SCR];
+            break;
+
         default:
             rc = -EINVAL;
             break;
-- 
2.51.0