From: Icenowy Zheng <uwu@icenowy.me>

U-Boot queries the FIFO water level to reduce checking status register
when doing PIO SD card operation.

Report a FIFO water level of 1 when data is ready, to prevent the code
from trying to read 0 words from the FIFO each time.

Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
Message-id: 20220520124200.2112699-1-uwu@icenowy.me
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/sd/allwinner-sdhost.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/sd/allwinner-sdhost.c b/hw/sd/allwinner-sdhost.c
index 041e45c6804..455d6eabf64 100644
--- a/hw/sd/allwinner-sdhost.c
+++ b/hw/sd/allwinner-sdhost.c
@@ -114,7 +114,9 @@ enum {
 };
 
 enum {
+    SD_STAR_FIFO_EMPTY      = (1 << 2),
     SD_STAR_CARD_PRESENT    = (1 << 8),
+    SD_STAR_FIFO_LEVEL_1    = (1 << 17),
 };
 
 enum {
@@ -467,6 +469,11 @@ static uint64_t allwinner_sdhost_read(void *opaque, hwaddr offset,
         break;
     case REG_SD_STAR:      /* Status */
         res = s->status;
+        if (sdbus_data_ready(&s->sdbus)) {
+            res |= SD_STAR_FIFO_LEVEL_1;
+        } else {
+            res |= SD_STAR_FIFO_EMPTY;
+        }
         break;
     case REG_SD_FWLR:      /* FIFO Water Level */
         res = s->fifo_wlevel;
-- 
2.25.1