hw/char/pl011: Warn when using disabled transmitter

We shouldn't transmit characters when the full UART or its
transmitter is disabled. However we don't want to break the
possibly incomplete "my first bare metal assembly program"s,
so we choose to simply display a warning when this occurs.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240719181041.49545-9-philmd@linaro.org>

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index 0f9a5cd16d6cafc221e1c29090eeb4cf2f385be3..f0df58f7a98e002d037d24529f9edd6fa4d4641d 100644 (file)
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -85,7 +85,9 @@ DeviceState *pl011_create(hwaddr addr, qemu_irq irq, Chardev *chr)
 #define CR_OUT1     (1 << 12)
 #define CR_RTS      (1 << 11)
 #define CR_DTR      (1 << 10)
+#define CR_TXE      (1 << 8)
 #define CR_LBE      (1 << 7)
+#define CR_UARTEN   (1 << 0)
 
 /* Integer Baud Rate Divider, UARTIBRD */
 #define IBRD_MASK 0x3f
@@ -223,7 +225,14 @@ static void pl011_loopback_tx(PL011State *s, uint32_t value)
 
 static void pl011_write_txdata(PL011State *s, uint8_t data)
 {
-    /* ??? Check if transmitter is enabled.  */
+    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");
+    }
 
     /*
      * XXX this blocks entire thread. Rewrite to use