[PATCH v5 04/15] emul/ns16x50: implement DLL/DLM registers

[dmukhin@xxxxxxx]

From: Denis Mukhin <dmukhin@xxxxxxxx> 

Add DLL/DLM registers emulation.

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

Add stub for ns16x50_dlab_get() helper.

Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes since v4:
- new patch
---
 xen/common/emul/vuart/ns16x50.c | 36 ++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/xen/common/emul/vuart/ns16x50.c b/xen/common/emul/vuart/ns16x50.c
index f0479e1022fb..f9f307a4ad24 100644
--- a/xen/common/emul/vuart/ns16x50.c
+++ b/xen/common/emul/vuart/ns16x50.c
@@ -85,14 +85,24 @@ struct vuart_ns16x50 {
     spinlock_t lock;                    /* Protection */
 };
 
+static inline uint8_t cf_check ns16x50_dlab_get(const struct vuart_ns16x50 
*vdev)
+{
+    return 0;
+}
+
 /*
  * Emulate 8-bit write access to ns16x50 register.
  */
 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;
 
+    if ( ns16x50_dlab_get(vdev) && (reg == UART_DLL || reg == UART_DLM) )
+        regs[NS16X50_REGS_NUM + reg] = val;
+
     return rc;
 }
 
@@ -103,8 +113,16 @@ static int ns16x50_io_write8(
 static int ns16x50_io_write16(
     struct vuart_ns16x50 *vdev, uint32_t reg, uint16_t *data)
 {
+    uint16_t val = *data;
     int rc = -EINVAL;
 
+    if ( ns16x50_dlab_get(vdev) && reg == UART_DLL )
+    {
+        vdev->regs[NS16X50_REGS_NUM + UART_DLL] = val & 0xff;
+        vdev->regs[NS16X50_REGS_NUM + UART_DLM] = (val >> 8) & 0xff;
+        rc = 0;
+    }
+
     return rc;
 }
 
@@ -140,9 +158,13 @@ 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 = 0xff;
     int rc = 0;
 
+    if ( ns16x50_dlab_get(vdev) && (reg == UART_DLL || reg == UART_DLM) )
+        val = regs[NS16X50_REGS_NUM + reg];
+
     *data = val;
 
     return rc;
@@ -157,6 +179,13 @@ static int ns16x50_io_read16(
     uint16_t val = 0xffff;
     int rc = -EINVAL;
 
+    if ( ns16x50_dlab_get(vdev) && 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;
@@ -237,7 +266,7 @@ static int cf_check ns16x50_io_handle(
         goto out;
     }
 
-    dlab = 0;
+    dlab = ns16x50_dlab_get(vdev);
     if ( reg >= NS16X50_REGS_NUM )
     {
         ns16x50_err(vdev, "%c io 0x%04x %d: DLAB=%d %02"PRIx32" 0x%08"PRIx32": 
not implemented\n",
@@ -274,12 +303,17 @@ out:
 
 static int ns16x50_init(void *arg)
 {
+    const uint16_t divisor = (UART_CLOCK_HZ / 115200) >> 4;
     struct vuart_ns16x50 *vdev = arg;
     const struct vuart_info *info = vdev->info;
     struct domain *d = vdev->owner;
 
     ASSERT(vdev);
 
+    /* NB: report 115200 baud rate. */
+    vdev->regs[NS16X50_REGS_NUM + UART_DLL] = divisor & 0xff;
+    vdev->regs[NS16X50_REGS_NUM + UART_DLM] = (divisor >> 8) & 0xff;
+
     register_portio_handler(d, info->base_addr, info->size, ns16x50_io_handle);
 
     return 0;
-- 
2.51.0