From: Iris Johnson <iris@modwiz.com>

Currently the Exynos 4210 UART code always reports available FIFO space
when the backend checks for buffer space. When the FIFO is disabled this
is behavior causes the backend chardev code to replace the data before the
guest can read it.

This patch changes adds the logic to report the capacity properly when the
FIFO is not being used.

Buglink: https://bugs.launchpad.net/qemu/+bug/1913344
Signed-off-by: Iris Johnson <iris@modwiz.com>
Message-id: 20210128033655.1029577-1-iris@modwiz.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/char/exynos4210_uart.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/char/exynos4210_uart.c b/hw/char/exynos4210_uart.c
index 6361df2ad3c..9b21d201b34 100644
--- a/hw/char/exynos4210_uart.c
+++ b/hw/char/exynos4210_uart.c
@@ -553,7 +553,11 @@ static int exynos4210_uart_can_receive(void *opaque)
 {
     Exynos4210UartState *s = (Exynos4210UartState *)opaque;
 
-    return fifo_empty_elements_number(&s->rx);
+    if (s->reg[I_(UFCON)] & UFCON_FIFO_ENABLE) {
+        return fifo_empty_elements_number(&s->rx);
+    } else {
+        return !(s->reg[I_(UTRSTAT)] & UTRSTAT_Rx_BUFFER_DATA_READY);
+    }
 }
 
 static void exynos4210_uart_receive(void *opaque, const uint8_t *buf, int size)
-- 
2.20.1