[PATCH v2 08/11] hw/char/pl011: Warn when using disabled transmitter

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

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>
---
 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 e2e3d48b91..03dce0a1ec 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, const uint8_t *buf, int length)
 {
-    /* ??? Check if transmitter is enabled.  */
+    if (!(s->cr & CR_UARTEN)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "PL011 write data but UART disabled\n");
+    }
+    if (!(s->cr & CR_TXE)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "PL011 write data but TX disabled\n");
+    }
 
     /* XXX this blocks entire thread. Rewrite to use
      * qemu_chr_fe_write and background I/O callbacks */
-- 
2.38.1