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authorJean Delvare <khali@linux-fr.org>2010-03-02 06:23:42 -0500
committerJean Delvare <khali@linux-fr.org>2010-03-02 06:23:42 -0500
commitb5527a7766f0505dc72efe3cefe5e9dea826f611 (patch)
tree0282f6f16a1377a8070d317cc385541e9c651b2c /Documentation/i2c
parent6d376fcc28d98f7f8f652755ae4dca1ff7240563 (diff)
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>
Diffstat (limited to 'Documentation/i2c')
-rw-r--r--Documentation/i2c/smbus-protocol16
1 files changed, 16 insertions, 0 deletions
diff --git a/Documentation/i2c/smbus-protocol b/Documentation/i2c/smbus-protocol
index 9df47441f0e7..7c19d1a2bea0 100644
--- a/Documentation/i2c/smbus-protocol
+++ b/Documentation/i2c/smbus-protocol
@@ -185,6 +185,22 @@ the protocol. All ARP communications use slave address 0x61 and
185require PEC checksums. 185require PEC checksums.
186 186
187 187
188SMBus Alert
189===========
190
191SMBus Alert was introduced in Revision 1.0 of the specification.
192
193The SMBus alert protocol allows several SMBus slave devices to share a
194single interrupt pin on the SMBus master, while still allowing the master
195to know which slave triggered the interrupt.
196
197This is implemented the following way in the Linux kernel:
198* I2C bus drivers which support SMBus alert should call
199 i2c_setup_smbus_alert() to setup SMBus alert support.
200* I2C drivers for devices which can trigger SMBus alerts should implement
201 the optional alert() callback.
202
203
188I2C Block Transactions 204I2C Block Transactions
189====================== 205======================
190 206