[PATCH v1 1/2] i3c: master: svc: Fix missed IBI after false SLVSTART on NPCM845

[Stanley Chu]

From: Stanley Chu <yschu@xxxxxxxxxxx>

The NPCM845 I3C controller may raise a false SLVSTART interrupt. The
handler first latches MSTATUS and then clears SLVSTART. If a real IBI
request arrives after the handler latches MSTATUS but before it clears
the SLVSTART interrupt status, HW sets the SLVREQ state. However, the
handler still relies on the stale MSTATUS snapshot, returns early, and
misses the real IBI. No further interrupt is generated for this pending
IBI.

Re-read MSTATUS to obtain the latest state and avoid missing a real IBI
due to this race condition.

Fixes: 4dd12e944f07 ("i3c: master: svc: Fix npcm845 invalid slvstart event")
Signed-off-by: Stanley Chu <yschu@xxxxxxxxxxx>
---
 drivers/i3c/master/svc-i3c-master.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
index b84b324e4111..7d88e8fe3742 100644
--- a/drivers/i3c/master/svc-i3c-master.c
+++ b/drivers/i3c/master/svc-i3c-master.c
@@ -672,10 +672,18 @@ static irqreturn_t svc_i3c_master_irq_handler(int irq, void *dev_id)
 	/* Clear the interrupt status */
 	writel(SVC_I3C_MINT_SLVSTART, master->regs + SVC_I3C_MSTATUS);
 
-	/* Ignore the false event */
-	if (svc_has_quirk(master, SVC_I3C_QUIRK_FALSE_SLVSTART) &&
-	    !SVC_I3C_MSTATUS_STATE_SLVREQ(active))
-		return IRQ_HANDLED;
+	if (svc_has_quirk(master, SVC_I3C_QUIRK_FALSE_SLVSTART)) {
+		/*
+		 * Re-read MSTATUS to obtain the latest state and avoid
+		 * missing an IBI that arrives after MSTATUS is latched
+		 * but before SLVSTART is cleared.
+		 */
+		active = readl(master->regs + SVC_I3C_MSTATUS);
+
+		/* Ignore the false event */
+		if (!SVC_I3C_MSTATUS_STATE_SLVREQ(active))
+			return IRQ_HANDLED;
+	}
 
 	/*
 	 * The SDA line remains low until the request is processed.
-- 
2.34.1