[PATCH-for-8.2 v4 06/10] 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 | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index 30309337b1..9c43cb47bf 100644
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -76,6 +76,10 @@ DeviceState *pl011_create(hwaddr addr, qemu_irq irq, Chardev 
*chr)
 #define LCR_FEN     (1 << 4)
 #define LCR_BRK     (1 << 0)
 
+/* Control Register, UARTCR */
+#define CR_TXE      (1 << 8)
+#define CR_UARTEN   (1 << 0)
+
 static const unsigned char pl011_id_arm[8] =
   { 0x11, 0x10, 0x14, 0x00, 0x0d, 0xf0, 0x05, 0xb1 };
 static const unsigned char pl011_id_luminary[8] =
@@ -151,7 +155,12 @@ static inline void pl011_reset_tx_fifo(PL011State *s)
 
 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