can: hi311x: Use level-triggered interrupt

If the hi3110 shares the SPI bus with another traffic-intensive device
and packets are received in high volume (by a separate machine sending
with "cangen -g 0 -i -x"), reception stops after a few minutes and the
counter in /proc/interrupts stops incrementing.  Bus state is "active".
Bringing the interface down and back up reconvenes the reception.  The
issue is not observed when the hi3110 is the sole device on the SPI bus.

Using a level-triggered interrupt makes the issue go away and lets the
hi3110 successfully receive 2 GByte over the course of 5 days while a
ks8851 Ethernet chip on the same SPI bus handles 6 GByte of traffic.

Unfortunately the hi3110 datasheet is mum on the trigger type.  The pin
description on page 3 only specifies the polarity (active high):
http://www.holtic.com/documents/371-hi-3110_v-rev-kpdf.do

Cc: Mathias Duckeck <m.duckeck@kunbus.de>
Cc: Akshay Bhat <akshay.bhat@timesys.com>
Cc: Casey Fitzpatrick <casey.fitzpatrick@timesys.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Documentation/devicetree/bindings/net/can/holt_hi311x.txt

@@ -17,7 +17,7 @@ Example:
 		reg = <1>;
 		clocks = <&clk32m>;
 		interrupt-parent = <&gpio4>;
-		interrupts = <13 IRQ_TYPE_EDGE_RISING>;
+		interrupts = <13 IRQ_TYPE_LEVEL_HIGH>;
 		vdd-supply = <&reg5v0>;
 		xceiver-supply = <&reg5v0>;
 	};

drivers/net/can/spi/hi311x.c

@@ -760,7 +760,7 @@ static int hi3110_open(struct net_device *net)
 {
 	struct hi3110_priv *priv = netdev_priv(net);
 	struct spi_device *spi = priv->spi;
-	unsigned long flags = IRQF_ONESHOT | IRQF_TRIGGER_RISING;
+	unsigned long flags = IRQF_ONESHOT | IRQF_TRIGGER_HIGH;
 	int ret;
 
 	ret = open_candev(net);