[PATCH v5 10/15] emul/ns16x50: implement SCR register

[dmukhin]

From: Denis Mukhin <dmuk...@ford.com> 

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 <dmuk...@ford.com>
---
Changes since v4:
- new 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 670c3c6dba9d..d57695564329 100644
--- a/xen/common/emul/vuart/ns16x50.c
+++ b/xen/common/emul/vuart/ns16x50.c
@@ -444,6 +444,11 @@ static int ns16x50_io_write8(
             break;
         }
 
+        /* NB: Firmware (e.g. OVMF) may rely on SCR presence. */
+        case UART_SCR:
+            regs[UART_SCR] = val;
+            break;
+
         case UART_LSR: /* RO */
         case UART_MSR: /* RO */
         default:
@@ -566,6 +571,10 @@ static int ns16x50_io_read8(
             regs[UART_MSR] &= ~UART_MSR_CHANGE;
             break;
 
+        case UART_SCR:
+            val = regs[UART_SCR];
+            break;
+
         default:
             rc = -EINVAL;
             break;
-- 
2.51.0