[PATCH v1] i3c: master: svc: Fix npcm845 FIFO_EMPTY quirk

[Stanley Chu <stanley.chuys@gmail.com>]

From: Stanley Chu <yschu@nuvoton.com>

Prefilling in private write transfers is only necessary when the FIFO
is empty. Otherwise, if the transfer is NACKed due to IBIWON and retries
continue, data may be prefilled again but could be lost because the FIFO
is not empty.

Fixes: 4008a74e0f9b ("i3c: master: svc: Fix npcm845 FIFO empty issue")
Signed-off-by: Stanley Chu <yschu@nuvoton.com>
---
 drivers/i3c/master/svc-i3c-master.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
index 7e1a7cb94b43..34b6e125b18a 100644
--- a/drivers/i3c/master/svc-i3c-master.c
+++ b/drivers/i3c/master/svc-i3c-master.c
@@ -104,6 +104,7 @@
 #define   SVC_I3C_MDATACTRL_TXTRIG_FIFO_NOT_FULL GENMASK(5, 4)
 #define   SVC_I3C_MDATACTRL_RXTRIG_FIFO_NOT_EMPTY 0
 #define   SVC_I3C_MDATACTRL_RXCOUNT(x) FIELD_GET(GENMASK(28, 24), (x))
+#define   SVC_I3C_MDATACTRL_TXCOUNT(x) FIELD_GET(GENMASK(20, 16), (x))
 #define   SVC_I3C_MDATACTRL_TXFULL BIT(30)
 #define   SVC_I3C_MDATACTRL_RXEMPTY BIT(31)
 
@@ -280,6 +281,13 @@ static inline bool is_events_enabled(struct svc_i3c_master *master, u32 mask)
 	return !!(master->enabled_events & mask);
 }
 
+static inline bool svc_i3c_master_tx_empty(struct svc_i3c_master *master)
+{
+	u32 reg = readl(master->regs + SVC_I3C_MDATACTRL);
+
+	return (SVC_I3C_MDATACTRL_TXCOUNT(reg) == 0);
+}
+
 static bool svc_i3c_master_error(struct svc_i3c_master *master)
 {
 	u32 mstatus, merrwarn;
@@ -1303,7 +1311,8 @@ static int svc_i3c_master_xfer(struct svc_i3c_master *master,
 		 * The only way to work around this hardware issue is to let the
 		 * FIFO start filling as soon as possible after EmitStartAddr.
 		 */
-		if (svc_has_quirk(master, SVC_I3C_QUIRK_FIFO_EMPTY) && !rnw && xfer_len) {
+		if (svc_has_quirk(master, SVC_I3C_QUIRK_FIFO_EMPTY) && !rnw && xfer_len &&
+		    svc_i3c_master_tx_empty(master)) {
 			u32 end = xfer_len > SVC_I3C_FIFO_SIZE ? 0 : SVC_I3C_MWDATAB_END;
 			u32 len = min_t(u32, xfer_len, SVC_I3C_FIFO_SIZE);
 
-- 
2.34.1