i2c-at91: Mark as broken

Mark the i2c-at91 driver BROKEN in Kconfig, and explain just
why it's broken.  (Summary:  hardware design issues.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index a9cab3e5b8bd..de95c75efb41 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -75,11 +75,19 @@ config I2C_AMD8111
 
 config I2C_AT91
         tristate "Atmel AT91 I2C Two-Wire interface (TWI)"
-        depends on ARCH_AT91 && EXPERIMENTAL
+        depends on ARCH_AT91 && EXPERIMENTAL && BROKEN
         help
           This supports the use of the I2C interface on Atmel AT91
           processors.
 
+          This driver is BROKEN because the controller which it uses
+          will easily trigger RX overrun and TX underrun errors.  Using
+          low I2C clock rates may partially work around those issues
+          on some systems.  Another serious problem is that there is no
+          documented way to issue repeated START conditions, as needed
+          to support combined I2C messages.  Use the i2c-gpio driver
+          unless your system can cope with those limitations.
+
 config I2C_AU1550
         tristate "Au1550/Au1200 SMBus interface"
         depends on SOC_AU1550 || SOC_AU1200