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[2/8] i2c: at91: add warning about transmission issues for some devices

Message ID 1346404884-18451-3-git-send-email-ludovic.desroches@atmel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Ludovic Desroches Aug. 31, 2012, 9:21 a.m. UTC 
From: Ludovic Desroches <ludovic.desroches@atmel.com>

Some devices don't have clock streching in transmission mode. It can
lead to premature stop sendings if the latency to write data in the
transmission register is too long. In this case, prefer the i2c-gpio
driver.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
---
 drivers/i2c/busses/Kconfig | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Voss, Nikolaus Sept. 3, 2012, 5:54 a.m. UTC | #1 
ludovic.desroches@atmel.com wrote on Friday, August 31, 2012 11:21 AM
> From: Ludovic Desroches <ludovic.desroches@atmel.com>
> 
> Some devices don't have clock streching in transmission mode. It can
> lead to premature stop sendings if the latency to write data in the
> transmission register is too long. In this case, prefer the i2c-gpio
> driver.
> 
> Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Nikolaus Voss <n.voss@weinmann.de>

> ---
>  drivers/i2c/busses/Kconfig | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index d9c4918..da77c37 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -300,6 +300,12 @@ config I2C_AT91
>  	  to support combined I2C messages.  Use the i2c-gpio driver
>  	  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"
>  	depends on MIPS_ALCHEMY
> --
> 1.7.11.3
diff mbox

Patch

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index d9c4918..da77c37 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -300,6 +300,12 @@  config I2C_AT91
 	  to support combined I2C messages.  Use the i2c-gpio driver
 	  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"
 	depends on MIPS_ALCHEMY