i2c: use an IRQ to report Host Notify events, not alert

The current SMBus Host Notify implementation relies on .alert() to
relay its notifications. However, the use cases where SMBus Host
Notify is needed currently is to signal data ready on touchpads.

This is closer to an IRQ than a custom API through .alert().
Given that the 2 touchpad manufacturers (Synaptics and Elan) that
use SMBus Host Notify don't put any data in the SMBus payload, the
concept actually matches one to one.

Benefits are multiple:
- simpler code and API: the client will just have an IRQ, and
  nothing needs to be added in the adapter beside internally
  enabling it.
- no more specific workqueue, the threading is handled by IRQ core
  directly (when required)
- no more races when removing the device (the drivers are already
  required to disable irq on remove)
- simpler handling for drivers: use plain regular IRQs
- no more dependency on i2c-smbus for i2c-i801 (and any other adapter)
- the IRQ domain is created automatically when the adapter exports
  the Host Notify capability
- the IRQ are assign only if ACPI, OF and the caller did not assign
  one already
- the domain is automatically destroyed on remove
- fewer lines of code (minus 20, yeah!)

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 82cf90945bb8..b2109c522dec 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -30,6 +30,7 @@
 #include <linux/device.h>	/* for struct device */
 #include <linux/sched.h>	/* for completion */
 #include <linux/mutex.h>
+#include <linux/irqdomain.h>		/* for Host Notify IRQ */
 #include <linux/of.h>		/* for struct device_node */
 #include <linux/swab.h>		/* for swab16 */
 #include <uapi/linux/i2c.h>
@@ -575,6 +576,8 @@ struct i2c_adapter {
 
 	struct i2c_bus_recovery_info *bus_recovery_info;
 	const struct i2c_adapter_quirks *quirks;
+
+	struct irq_domain *host_notify_domain;
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)
 
@@ -747,6 +750,7 @@ static inline u8 i2c_8bit_addr_from_msg(const struct i2c_msg *msg)
 	return (msg->addr << 1) | (msg->flags & I2C_M_RD ? 1 : 0);
 }
 
+int i2c_handle_smbus_host_notify(struct i2c_adapter *adap, unsigned short addr);
 /**
  * module_i2c_driver() - Helper macro for registering a modular I2C driver
  * @__i2c_driver: i2c_driver struct