[PATCH v4 4/5] hw/char/pl011: better handling of FIFO flags on LCR reset

[Evgeny Iakovlev <eiakovlev@linux.microsoft.com>]

Current FIFO handling code does not reset RXFE/RXFF flags when guest
resets FIFO by writing to UARTLCR register, although internal FIFO state
is reset to 0 read count. Actual guest-visible flag update will happen
only on next data read or write attempt. As a result of that any guest
that expects RXFE flag to be set (and RXFF to be cleared) after resetting
FIFO will never see that happen.

Signed-off-by: Evgeny Iakovlev <eiakovlev@linux.microsoft.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/char/pl011.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index ca7537d8ed..c15cb7af20 100644
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -92,6 +92,16 @@ static inline unsigned pl011_get_fifo_depth(PL011State *s)
     return pl011_is_fifo_enabled(s) ? PL011_FIFO_DEPTH : 1;
 }
 
+static inline void pl011_reset_fifo(PL011State *s)
+{
+    s->read_count = 0;
+    s->read_pos = 0;
+
+    /* Reset FIFO flags */
+    s->flags &= ~(PL011_FLAG_RXFF | PL011_FLAG_TXFF);
+    s->flags |= PL011_FLAG_RXFE | PL011_FLAG_TXFE;
+}
+
 static uint64_t pl011_read(void *opaque, hwaddr offset,
                            unsigned size)
 {
@@ -239,8 +249,7 @@ static void pl011_write(void *opaque, hwaddr offset,
     case 11: /* UARTLCR_H */
         /* Reset the FIFO state on FIFO enable or disable */
         if ((s->lcr ^ value) & 0x10) {
-            s->read_count = 0;
-            s->read_pos = 0;
+            pl011_reset_fifo(s);
         }
         if ((s->lcr ^ value) & 0x1) {
             int break_enable = value & 0x1;
@@ -450,12 +459,11 @@ static void pl011_reset(DeviceState *dev)
     s->ilpr = 0;
     s->ibrd = 0;
     s->fbrd = 0;
-    s->read_pos = 0;
-    s->read_count = 0;
     s->read_trigger = 1;
     s->ifl = 0x12;
     s->cr = 0x300;
-    s->flags = 0x90;
+    s->flags = 0;
+    pl011_reset_fifo(s);
 }
 
 static void pl011_class_init(ObjectClass *oc, void *data)
-- 
2.34.1