i2c: Add SMBus alert support

SMBus alert support. The SMBus alert protocol allows several SMBus
slave devices to share a single interrupt pin on the SMBus master,
while still allowing the master to know which slave triggered the
interrupt.

This is based on preliminary work by David Brownell. The key
difference between David's implementation and mine is that his was
part of i2c-core, while mine is split into a separate, standalone
module named i2c-smbus. The i2c-smbus module is meant to include
support for all SMBus extensions to the I2C protocol in the future.

The benefit of this approach is a zero cost for I2C bus segments which
do not need SMBus alert support. Where David's implementation
increased the size of struct i2c_adapter by 7% (40 bytes on i386),
mine doesn't touch it. Where David's implementation added over 150
lines of code to i2c-core (+10%), mine doesn't touch it. The only
change that touches all the users of the i2c subsystem is a new
callback in struct i2c_driver (common to both implementations.) I seem
to remember Trent was worried about the footprint of David'd
implementation, hopefully mine addresses the issue.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Trent Piepho <tpiepho@freescale.com>

2 files changed, 57 insertions, 0 deletions

diff --git a/include/linux/i2c-smbus.h b/include/linux/i2c-smbus.h
new file mode 100644
index 00000000000..63f57a8c8b3
--- /dev/null
+++ b/include/linux/i2c-smbus.h
@@ -0,0 +1,50 @@
+/*
+ * i2c-smbus.h - SMBus extensions to the I2C protocol
+ *
+ * Copyright (C) 2010 Jean Delvare <khali@linux-fr.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef _LINUX_I2C_SMBUS_H
+#define _LINUX_I2C_SMBUS_H
+
+#include <linux/i2c.h>
+
+
+/**
+ * i2c_smbus_alert_setup - platform data for the smbus_alert i2c client
+ * @alert_edge_triggered: whether the alert interrupt is edge (1) or level (0)
+ *              triggered
+ * @irq: IRQ number, if the smbus_alert driver should take care of interrupt
+ *              handling
+ *
+ * If irq is not specified, the smbus_alert driver doesn't take care of
+ * interrupt handling. In that case it is up to the I2C bus driver to either
+ * handle the interrupts or to poll for alerts.
+ *
+ * If irq is specified then it it crucial that alert_edge_triggered is
+ * properly set.
+ */
+struct i2c_smbus_alert_setup {
+        unsigned int            alert_edge_triggered:1;
+        int                     irq;
+};
+
+struct i2c_client *i2c_setup_smbus_alert(struct i2c_adapter *adapter,
+                                         struct i2c_smbus_alert_setup *setup);
+int i2c_handle_smbus_alert(struct i2c_client *ara);
+
+#endif /* _LINUX_I2C_SMBUS_H */
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 02fc617782e..476abd09c92 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -152,6 +152,13 @@ struct i2c_driver {
         int (*suspend)(struct i2c_client *, pm_message_t mesg);
         int (*resume)(struct i2c_client *);
 
+        /* Alert callback, for example for the SMBus alert protocol.
+         * The format and meaning of the data value depends on the protocol.
+         * For the SMBus alert protocol, there is a single bit of data passed
+         * as the alert response's low bit ("event flag").
+         */
+        void (*alert)(struct i2c_client *, unsigned int data);
+
         /* a ioctl like command that can be used to perform specific functions
          * with the device.
          */