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

Message ID 20240719181041.49545-9-philmd@linaro.org
State Superseded
Headers show
Series hw/char/pl011: Implement TX (async) FIFO to avoid blocking the main loop | expand

Commit Message

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

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 */