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>

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index a9cab3e..de95c75 100644 (file)
--- 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