i2c: do not enable fall back to Host Notify by default

Falling back unconditionally to HostNotify as primary client's interrupt
breaks some drivers which alter their functionality depending on whether
interrupt is present or not, so let's introduce a board flag telling I2C
core explicitly if we want wired interrupt or HostNotify-based one:
I2C_CLIENT_HOST_NOTIFY.

For DT-based systems we introduce "host-notify" property that we convert
to I2C_CLIENT_HOST_NOTIFY board flag.

Tested-by: Benjamin Tissoires <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>
Acked-by: Pali Rohár <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

Documentation/devicetree/bindings/i2c/i2c.txt

···
 	"irq" and "wakeup" names are recognized by I2C core, other names are
 	left to individual drivers.
 
+- host-notify
+	device uses SMBus host notify protocol instead of interrupt line.
+
 - multi-master
 	states that there is another master active on this bus. The OS can use
 	this information to adapt power management to keep the arbitration awake
···
 Binding may contain optional "interrupts" property, describing interrupts
 used by the device. I2C core will assign "irq" interrupt (or the very first
 interrupt if not using interrupt names) as primary interrupt for the slave.
+
+Alternatively, devices supporting SMbus Host Notify, and connected to
+adapters that support this feature, may use "host-notify" property. I2C
+core will create a virtual interrupt for Host Notify and assign it as
+primary interrupt for the slave.
 
 Also, if device is marked as a wakeup source, I2C core will set up "wakeup"
 interrupt for the device. If "wakeup" interrupt name is not present in the

drivers/i2c/i2c-core.c

···
 	if (!client->irq) {
 		int irq = -ENOENT;
 
-		if (dev->of_node) {
+		if (client->flags & I2C_CLIENT_HOST_NOTIFY) {
+			dev_dbg(dev, "Using Host Notify IRQ\n");
+			irq = i2c_smbus_host_notify_to_irq(client);
+		} else if (dev->of_node) {
 			irq = of_irq_get_byname(dev->of_node, "irq");
 			if (irq == -EINVAL || irq == -ENODATA)
 				irq = of_irq_get(dev->of_node, 0);
···
 		}
 		if (irq == -EPROBE_DEFER)
 			return irq;
-		/*
-		 * ACPI and OF did not find any useful IRQ, try to see
-		 * if Host Notify can be used.
-		 */
-		if (irq < 0) {
-			dev_dbg(dev, "Using Host Notify IRQ\n");
-			irq = i2c_smbus_host_notify_to_irq(client);
-		}
+
 		if (irq < 0)
 			irq = 0;
 
···
 	info.addr = addr;
 	info.of_node = of_node_get(node);
 	info.archdata = &dev_ad;
+
+	if (of_property_read_bool(node, "host-notify"))
+		info.flags |= I2C_CLIENT_HOST_NOTIFY;
 
 	if (of_get_property(node, "wakeup-source", NULL))
 		info.flags |= I2C_CLIENT_WAKE;

include/linux/i2c.h

···
 #define I2C_CLIENT_TEN		0x10	/* we have a ten bit chip address */
 					/* Must equal I2C_M_TEN below */
 #define I2C_CLIENT_SLAVE	0x20	/* we are the slave */
+#define I2C_CLIENT_HOST_NOTIFY	0x40	/* We want to use I2C host notify */
 #define I2C_CLIENT_WAKE		0x80	/* for board_info; true iff can wake */
 #define I2C_CLIENT_SCCB		0x9000	/* Use Omnivision SCCB protocol */
 					/* Must match I2C_M_STOP|IGNORE_NAK */