[PATCH v5 08/16] hw/char/pl011: Warn when using disabled transmitter

[Philippe Mathieu-Daudé]

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>
---
 hw/char/pl011.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index 5e44837206..c76283dccf 100644
--- 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 +225,12 @@ 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
      * qemu_chr_fe_write and background I/O callbacks */
-- 
2.41.0