can: rcar_canfd: rcar_canfd_handle_global_receive(): fix IRQ storm on…

… global FIFO receive

We are seeing an IRQ storm on the global receive IRQ line under heavy
CAN bus load conditions with both CAN channels enabled.

Conditions:

The global receive IRQ line is shared between can0 and can1, either of
the channels can trigger interrupt while the other channel's IRQ line
is disabled (RFIE).

When global a receive IRQ interrupt occurs, we mask the interrupt in
the IRQ handler. Clearing and unmasking of the interrupt is happening
in rx_poll(). There is a race condition where rx_poll() unmasks the
interrupt, but the next IRQ handler does not mask the IRQ due to
NAPIF_STATE_MISSED flag (e.g.: can0 RX FIFO interrupt is disabled and
can1 is triggering RX interrupt, the delay in rx_poll() processing
results in setting NAPIF_STATE_MISSED flag) leading to an IRQ storm.

This patch fixes the issue by checking IRQ active and enabled before
handling the IRQ on a particular channel.

Fixes: dd3bd23 ("can: rcar_canfd: Add Renesas R-Car CAN FD driver")
Suggested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/all/20221025155657.1426948-2-biju.das.jz@bp.renesas.com
Cc: stable@vger.kernel.org
[mkl: adjust commit message]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/rcar/rcar_canfd.c

@@ -1157,11 +1157,13 @@ static void rcar_canfd_handle_global_receive(struct rcar_canfd_global *gpriv, u3
 {
 	struct rcar_canfd_channel *priv = gpriv->ch[ch];
 	u32 ridx = ch + RCANFD_RFFIFO_IDX;
-	u32 sts;
+	u32 sts, cc;
 
 	/* Handle Rx interrupts */
 	sts = rcar_canfd_read(priv->base, RCANFD_RFSTS(gpriv, ridx));
-	if (likely(sts & RCANFD_RFSTS_RFIF)) {
+	cc = rcar_canfd_read(priv->base, RCANFD_RFCC(gpriv, ridx));
+	if (likely(sts & RCANFD_RFSTS_RFIF &&
+		   cc & RCANFD_RFCC_RFIE)) {
 		if (napi_schedule_prep(&priv->napi)) {
 			/* Disable Rx FIFO interrupts */
 			rcar_canfd_clear_bit(priv->base,