[PATCH v8 05/26] emul/ns16x50: implement DLL/DLM registers

[dmukhin@xxxxxxxx]

From: Denis Mukhin <dmukhin@xxxxxxxx>

Add DLL/DLM registers emulation.

DLL/DLM registers report hardcoded 115200 baud rate to the guest OS.

Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
 xen/common/emul/vuart/ns16x50.c | 82 +++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

diff --git a/xen/common/emul/vuart/ns16x50.c b/xen/common/emul/vuart/ns16x50.c
index 6e1cfecbaa55..80805ee6ecc6 100644
--- a/xen/common/emul/vuart/ns16x50.c
+++ b/xen/common/emul/vuart/ns16x50.c
@@ -119,8 +119,37 @@ static inline void ns16x50_unlock(struct vuart_ns16x50 
*vdev,
 static int ns16x50_io_write8(
     struct vuart_ns16x50 *vdev, uint32_t reg, uint8_t *data)
 {
+    uint8_t *regs = vdev->regs;
+    uint8_t val = *data;
     int rc = 0;
 
+    switch ( reg )
+    {
+    case UART_THR: /* DLAB=0 --> UART_RBR, DLAB=1 --> UART_DLL */
+        /* DLAB=1 */
+        if ( regs[UART_LCR] & UART_LCR_DLAB )
+        {
+            regs[NS16X50_REGS_NUM + UART_DLL] = val;
+            break;
+        }
+
+        /* DLAB=0 */
+        break;
+
+    case UART_IER: /* DLAB=0 --> UART_IER, DLAB=1 --> UART_DLM */
+        /* DLAB=1 */
+        if ( regs[UART_LCR] & UART_LCR_DLAB )
+        {
+            regs[NS16X50_REGS_NUM + UART_DLM] = val;
+        }
+        /* DLAB=0 */
+        break;
+
+    default:
+        rc = -EINVAL;
+        break;
+    }
+
     return rc;
 }
 
@@ -131,8 +160,17 @@ static int ns16x50_io_write8(
 static int ns16x50_io_write16(
     struct vuart_ns16x50 *vdev, uint32_t reg, uint16_t *data)
 {
+    uint8_t *regs = vdev->regs;
+    uint16_t val = *data;
     int rc = -EINVAL;
 
+    if ( (regs[UART_LCR] & UART_LCR_DLAB) && reg == UART_DLL )
+    {
+        vdev->regs[NS16X50_REGS_NUM + UART_DLL] = val & UINT8_MAX;
+        vdev->regs[NS16X50_REGS_NUM + UART_DLM] = (val >> 8) & UINT8_MAX;
+        rc = 0;
+    }
+
     return rc;
 }
 
@@ -168,9 +206,39 @@ static int ns16x50_io_write(
 static int ns16x50_io_read8(
     struct vuart_ns16x50 *vdev, uint32_t reg, uint8_t *data)
 {
+    uint8_t *regs = vdev->regs;
     uint8_t val = UINT8_MAX;
     int rc = 0;
 
+    switch ( reg )
+    {
+    case UART_RBR: /* DLAB=0 --> UART_RBR, DLAB=1 --> UART_DLL */
+        /* DLAB=1 */
+        if ( regs[UART_LCR] & UART_LCR_DLAB )
+        {
+            val = regs[NS16X50_REGS_NUM + UART_DLL];
+            break;
+        }
+
+        /* DLAB=0 */
+        break;
+
+    case UART_IER: /* DLAB=0 --> UART_IER, DLAB=1 --> UART_DLM */
+        /* DLAB=1 */
+        if ( regs[UART_LCR] & UART_LCR_DLAB )
+        {
+            val = regs[NS16X50_REGS_NUM + UART_DLM];
+            break;
+        }
+
+        /* DLAB=0 */
+        break;
+
+    default:
+        rc = -EINVAL;
+        break;
+    }
+
     *data = val;
 
     return rc;
@@ -182,9 +250,17 @@ static int ns16x50_io_read8(
 static int ns16x50_io_read16(
     struct vuart_ns16x50 *vdev, uint32_t reg, uint16_t *data)
 {
+    uint8_t *regs = vdev->regs;
     uint16_t val = UINT16_MAX;
     int rc = -EINVAL;
 
+    if ( (regs[UART_LCR] & UART_LCR_DLAB) && reg == UART_DLL )
+    {
+        val = vdev->regs[NS16X50_REGS_NUM + UART_DLM] << 8 |
+              vdev->regs[NS16X50_REGS_NUM + UART_DLL];
+        rc = 0;
+    }
+
     *data = val;
 
     return rc;
@@ -310,7 +386,13 @@ static int cf_check ns16x50_io_handle(
 
 static void ns16x50_reset(struct vuart_ns16x50 *vdev)
 {
+    const uint16_t divisor = (UART_CLOCK_HZ / 115200) >> 4;
+
     memset(vdev->regs, 0, sizeof(vdev->regs));
+
+    /* NB: report 115200 baud rate. */
+    vdev->regs[NS16X50_REGS_NUM + UART_DLL] = divisor & UINT8_MAX;
+    vdev->regs[NS16X50_REGS_NUM + UART_DLM] = (divisor >> 8) & UINT8_MAX;
 }
 
 static int ns16x50_init(void *arg)
-- 
2.56.0