[PATCH v6 5/7] hw/char/pl011: Consider TX FIFO overrun error

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

When transmission is disabled, characters are still queued
to the FIFO which eventually overruns. Report that error
condition in the status register.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/char/pl011.c      | 20 ++++++++++++++++++++
 hw/char/trace-events |  2 ++
 2 files changed, 22 insertions(+)

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index 447f185e2d5..ef39ab666a2 100644
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -61,6 +61,9 @@ DeviceState *pl011_create(hwaddr addr, qemu_irq irq, Chardev *chr)
 /* Data Register, UARTDR */
 #define DR_BE   (1 << 10)
 
+/* Receive Status Register/Error Clear Register, UARTRSR/UARTECR */
+#define RSR_OE  (1 << 3)
+
 /* Interrupt status bits in UARTRIS, UARTMIS, UARTIMSC */
 #define INT_OE (1 << 10)
 #define INT_BE (1 << 9)
@@ -158,6 +161,16 @@ static inline unsigned pl011_get_fifo_depth(PL011State *s)
     return pl011_is_fifo_enabled(s) ? PL011_FIFO_DEPTH : 1;
 }
 
+static bool pl011_is_tx_fifo_full(PL011State *s)
+{
+    if (pl011_is_fifo_enabled(s)) {
+        trace_pl011_fifo_tx_is_full("FIFO", fifo8_is_full(&s->xmit_fifo));
+        return fifo8_is_full(&s->xmit_fifo);
+    }
+    trace_pl011_fifo_tx_is_full("CHAR", !fifo8_is_empty(&s->xmit_fifo));
+    return !fifo8_is_empty(&s->xmit_fifo);
+}
+
 static inline void pl011_reset_rx_fifo(PL011State *s)
 {
     s->read_count = 0;
@@ -264,6 +277,13 @@ static void pl011_write_txdata(PL011State *s, uint8_t data)
                       "PL011 data written to disabled TX UART\n");
     }
 
+    if (pl011_is_tx_fifo_full(s)) {
+        /* The FIFO is already full. Content remains valid. */
+        trace_pl011_fifo_tx_overrun();
+        s->rsr |= RSR_OE;
+        return;
+    }
+
     trace_pl011_fifo_tx_put(data);
     pl011_loopback_tx(s, data);
     fifo8_push(&s->xmit_fifo, data);
diff --git a/hw/char/trace-events b/hw/char/trace-events
index dd635ac6012..8234f3afa13 100644
--- a/hw/char/trace-events
+++ b/hw/char/trace-events
@@ -67,9 +67,11 @@ pl011_fifo_enable(bool enable) "enable:%u"
 pl011_fifo_is_enabled(bool enabled) "enabled:%u"
 pl011_fifo_rx_put(uint32_t c, int read_count) "new char 0x%02x read_count now %d"
 pl011_fifo_rx_full(void) "RX FIFO now full, RXFF set"
+pl011_fifo_tx_is_full(const char *desc, bool full) "mode:%s full:%u"
 pl011_fifo_tx_put(uint8_t byte) "TX FIFO push char [0x%02x]"
 pl011_fifo_tx_xmit_used(unsigned sent) "TX FIFO used %u chars"
 pl011_fifo_tx_xmit_consumed(unsigned sent) "TX FIFO consumed %u chars"
+pl011_fifo_tx_overrun(void) "TX FIFO overrun"
 pl011_baudrate_change(unsigned int baudrate, uint64_t clock, uint32_t ibrd, uint32_t fbrd) "new baudrate %u (clk: %" PRIu64 "hz, ibrd: %" PRIu32 ", fbrd: %" PRIu32 ")"
 
 # cmsdk-apb-uart.c
-- 
2.47.1