i2c: at91: add new driver
This driver has the following properties compared to the old driver:
1. Support for multiple interfaces.
2. Interrupt driven I/O as opposed to polling/busy waiting.
3. Support for _one_ repeated start (Sr) condition, which is enough
for most real-world applications including all SMBus transfer types.
(The hardware does not support issuing arbitrary Sr conditions on the
bus.)
testing: SoC: at91sam9g45
- BQ20Z80 battery SMBus client.
- on a 2.6.38 kernel with several i2c clients (temp-sensor,
audio-codec, touchscreen-controller, w1-bridge, io-expanders)
Signed-off-by: Nikolaus Voss <n.voss@weinmann.de>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Tested-by: Hubert Feurstein <h.feurstein@gmail.com>
Tested-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Reviewed-by: Nicolas Ferre <nicolas.ferre@atmel.com>
[wsa: squashed with the following patches from Ludovic to have some flaws
fixed:
i2c: at91: use managed resources
i2c: at91: add warning about transmission issues for some devices
i2c: at91: use an id table for SoC dependent parameters
]
Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index b4aaa1b..da77c37 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -290,18 +290,21 @@
config I2C_AT91
tristate "Atmel AT91 I2C Two-Wire interface (TWI)"
- depends on ARCH_AT91 && EXPERIMENTAL && BROKEN
+ depends on ARCH_AT91 && EXPERIMENTAL
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
+ A serious problem is that there is no documented way to issue
+ repeated START conditions for more than two messages, as needed
to support combined I2C messages. Use the i2c-gpio driver
- unless your system can cope with those limitations.
+ unless your system can cope with this limitation.
+
+ Caution! at91rm9200, at91sam9261, at91sam9260, at91sam9263 devices
+ don't have clock stretching in transmission mode. For that reason,
+ you can encounter underrun issues causing premature stop sendings if
+ the latency to fill the transmission register is too long. If you
+ are facing this situation, use the i2c-gpio driver.
config I2C_AU1550
tristate "Au1550/Au1200/Au1300 SMBus interface"