platform/chrome: Add a new interrupt path for cros_ec_lpc

This commit allows cros_ec_lpc to register a direct IRQ instead of relying
on the ACPI notification chain to receive MKBP events.

This change is done in the interest of allowing reduced jitter in the
communication path between the CrOS EC and the host for receiving sensor
data.
Signed-off-by: Enrico Granata <egranata@chromium.org>
Signed-off-by: Benson Leung <bleung@chromium.org>

drivers/platform/chrome/cros_ec_lpc.c

@@ -25,6 +25,7 @@
 #include <linux/dmi.h>
 #include <linux/delay.h>
 #include <linux/io.h>
+#include <linux/interrupt.h>
 #include <linux/mfd/cros_ec.h>
 #include <linux/mfd/cros_ec_commands.h>
 #include <linux/module.h>
@@ -249,7 +250,7 @@ static int cros_ec_lpc_probe(struct platform_device *pdev)
 	acpi_status status;
 	struct cros_ec_device *ec_dev;
 	u8 buf[2];
-	int ret;
+	int irq, ret;
 
 	if (!devm_request_region(dev, EC_LPC_ADDR_MEMMAP, EC_MEMMAP_SIZE,
 				 dev_name(dev))) {
@@ -288,6 +289,18 @@ static int cros_ec_lpc_probe(struct platform_device *pdev)
 			   sizeof(struct ec_response_get_protocol_info);
 	ec_dev->dout_size = sizeof(struct ec_host_request);
 
+	/*
+	 * Some boards do not have an IRQ allotted for cros_ec_lpc,
+	 * which makes ENXIO an expected (and safe) scenario.
+	 */
+	irq = platform_get_irq(pdev, 0);
+	if (irq > 0)
+		ec_dev->irq = irq;
+	else if (irq != -ENXIO) {
+		dev_err(dev, "couldn't retrieve IRQ number (%d)\n", irq);
+		return irq;
+	}
+
 	ret = cros_ec_register(ec_dev);
 	if (ret) {
 		dev_err(dev, "couldn't register ec_dev (%d)\n", ret);