[v5,14/16] hw/char/pl011: Consider TX FIFO overrun error

Commit Message

Philippe Mathieu-Daudé July 19, 2024, 6:10 p.m. UTC

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 <[e-mail]>
---
 hw/char/pl011.c      | 17 +++++++++++++++++
 hw/char/trace-events |  1 +
 2 files changed, 18 insertions(+)

Patch

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index 6394d6eb36..b8cde03f98 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)
@@ -232,6 +235,13 @@  static gboolean pl011_xmit(void *do_not_use, GIOCondition cond, void *opaque)
     int bytes_consumed;
     uint8_t data;
 
+    if (!(s->cr & CR_UARTEN)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "PL011 data written to disabled UART\n");
+    }
+    if (!(s->cr & CR_TXE)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "PL011 data written to disabled TX UART\n");
+    }
+
     data = fifo8_pop(&s->xmit_fifo);
     bytes_consumed = 1;
 
@@ -257,6 +267,13 @@  static void pl011_write_txdata(PL011State *s, uint8_t data)
         qemu_log_mask(LOG_GUEST_ERROR, "PL011 data written to disabled TX UART\n");
     }
 
+    if (fifo8_is_full(&s->xmit_fifo)) {
+        /* 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 30d06a2383..4a9c0bd271 100644
--- a/hw/char/trace-events
+++ b/hw/char/trace-events
@@ -62,6 +62,7 @@  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_put(uint8_t byte) "TX FIFO push char [0x%02x]"
 pl011_fifo_tx_xmit(int count) "TX FIFO pop %d 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