[PATCH v2] hw/char: disable ibex uart receive if the buffer is full

[Alexander Wagner <alexander.wagner@ulal.de>]

Not disabling the UART leads to QEMU overwriting the UART receive buffer with
the newest received byte. The rx_level variable is added to allow the use of
the existing OpenTitan driver libraries.

Signed-off-by: Alexander Wagner <alexander.wagner@ulal.de>
---
 hw/char/ibex_uart.c         | 23 ++++++++++++++++++-----
 include/hw/char/ibex_uart.h |  4 ++++
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/hw/char/ibex_uart.c b/hw/char/ibex_uart.c
index 89f1182c9b..bc3e2482bc 100644
--- a/hw/char/ibex_uart.c
+++ b/hw/char/ibex_uart.c
@@ -66,7 +66,8 @@ static int ibex_uart_can_receive(void *opaque)
 {
     IbexUartState *s = opaque;
 
-    if (s->uart_ctrl & R_CTRL_RX_ENABLE_MASK) {
+    if ((s->uart_ctrl & R_CTRL_RX_ENABLE_MASK)
+           && !(s->uart_status & R_STATUS_RXFULL_MASK)) {
         return 1;
     }
 
@@ -83,6 +84,11 @@ static void ibex_uart_receive(void *opaque, const uint8_t *buf, int size)
 
     s->uart_status &= ~R_STATUS_RXIDLE_MASK;
     s->uart_status &= ~R_STATUS_RXEMPTY_MASK;
+    /* The RXFULL is set after receiving a single byte
+     * as the FIFO buffers are not yet implemented.
+     */
+    s->uart_status |= R_STATUS_RXFULL_MASK;
+    s->rx_level += 1;
 
     if (size > rx_fifo_level) {
         s->uart_intr_state |= R_INTR_STATE_RX_WATERMARK_MASK;
@@ -199,6 +205,7 @@ static void ibex_uart_reset(DeviceState *dev)
     s->uart_timeout_ctrl = 0x00000000;
 
     s->tx_level = 0;
+    s->rx_level = 0;
 
     s->char_tx_time = (NANOSECONDS_PER_SECOND / 230400) * 10;
 
@@ -243,11 +250,15 @@ static uint64_t ibex_uart_read(void *opaque, hwaddr addr,
 
     case R_RDATA:
         retvalue = s->uart_rdata;
-        if (s->uart_ctrl & R_CTRL_RX_ENABLE_MASK) {
+        if ((s->uart_ctrl & R_CTRL_RX_ENABLE_MASK) && (s->rx_level > 0)) {
             qemu_chr_fe_accept_input(&s->chr);
 
-            s->uart_status |= R_STATUS_RXIDLE_MASK;
-            s->uart_status |= R_STATUS_RXEMPTY_MASK;
+            s->rx_level -= 1;
+            s->uart_status &= ~R_STATUS_RXFULL_MASK;
+            if (s->rx_level == 0) {
+                s->uart_status |= R_STATUS_RXIDLE_MASK;
+                s->uart_status |= R_STATUS_RXEMPTY_MASK;
+            }
         }
         break;
     case R_WDATA:
@@ -261,7 +272,8 @@ static uint64_t ibex_uart_read(void *opaque, hwaddr addr,
     case R_FIFO_STATUS:
         retvalue = s->uart_fifo_status;
 
-        retvalue |= s->tx_level & 0x1F;
+        retvalue |= (s->rx_level & 0x1F) << R_FIFO_STATUS_RXLVL_SHIFT;
+        retvalue |= (s->tx_level & 0x1F) << R_FIFO_STATUS_TXLVL_SHIFT;
 
         qemu_log_mask(LOG_UNIMP,
                       "%s: RX fifos are not supported\n", __func__);
@@ -364,6 +376,7 @@ static void ibex_uart_write(void *opaque, hwaddr addr,
         s->uart_fifo_ctrl = value;
 
         if (value & R_FIFO_CTRL_RXRST_MASK) {
+            s->rx_level = 0;
             qemu_log_mask(LOG_UNIMP,
                           "%s: RX fifos are not supported\n", __func__);
         }
diff --git a/include/hw/char/ibex_uart.h b/include/hw/char/ibex_uart.h
index 03d19e3f6f..546f958eb8 100644
--- a/include/hw/char/ibex_uart.h
+++ b/include/hw/char/ibex_uart.h
@@ -62,6 +62,8 @@ REG32(FIFO_CTRL, 0x1c)
     FIELD(FIFO_CTRL, RXILVL, 2, 3)
     FIELD(FIFO_CTRL, TXILVL, 5, 2)
 REG32(FIFO_STATUS, 0x20)
+    FIELD(FIFO_STATUS, TXLVL, 0, 5)
+    FIELD(FIFO_STATUS, RXLVL, 16, 5)
 REG32(OVRD, 0x24)
 REG32(VAL, 0x28)
 REG32(TIMEOUT_CTRL, 0x2c)
@@ -82,6 +84,8 @@ struct IbexUartState {
     uint8_t tx_fifo[IBEX_UART_TX_FIFO_SIZE];
     uint32_t tx_level;
 
+    uint32_t rx_level;
+
     QEMUTimer *fifo_trigger_handle;
     uint64_t char_tx_time;
 
-- 
2.25.1