Re: [PATCH] arm64: dts: imx8mq-zii-ultra: Operate I2C at 100kHz

[Angus Ainslie <angus@akkea.ca>]

Hi Lucas

On 2019-05-13 07:07, Lucas Stach wrote:
> Hi Fabio,
> 
> Am Montag, den 13.05.2019, 11:02 -0300 schrieb Fabio Estevam:
>> According to the i.MX8M errata document [1], there is an I2C spec
>> violation when the I2C clock frequency is 400 kHz:
>> 
>> "e7805: I2C: When the I2C clock speed is configured for 400 kHz, the
>> SCL low period violates the I2C spec of 1.3 uS min"
> 
>> Avoid this problem by running I2C at 100 kHz instead.
> 
> Does this fix a real bug? The same issue is present with the i.MX6 I2C
> controllers, but we are still running a lot of i2c busses on i.MX6
> based boards at 400kHz, with no issues whatsoever.
> 

We've definitely seen issues running at 400kHz with the librem5 devkit 
and it's using the i.MX8MQ.

Angus


> Regards,
> Lucas
> 
>> [1] https://www.nxp.com/docs/en/errata/IMX8MDQLQ_1N14W.pdf
>> 
>> Signed-off-by: Fabio Estevam <festevam@gmail.com>
>> ---
>>  arch/arm64/boot/dts/freescale/imx8mq-zii-ultra.dtsi | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>> 
>> diff --git a/arch/arm64/boot/dts/freescale/imx8mq-zii-ultra.dtsi
>> b/arch/arm64/boot/dts/freescale/imx8mq-zii-ultra.dtsi
>> index 7a1706f969f0..8603fb1a78d0 100644
>> --- a/arch/arm64/boot/dts/freescale/imx8mq-zii-ultra.dtsi
>> +++ b/arch/arm64/boot/dts/freescale/imx8mq-zii-ultra.dtsi
>> @@ -253,14 +253,14 @@
>>  };
>>  
>>  &i2c1 {
>> -	clock-frequency = <400000>;
>> +	clock-frequency = <100000>;
>>  	pinctrl-names = "default";
>>  	pinctrl-0 = <&pinctrl_i2c1>;
>>  	status = "okay";
>>  };
>>  
>>  &i2c2 {
>> -	clock-frequency = <400000>;
>> +	clock-frequency = <100000>;
>>  	pinctrl-names = "default";
>>  	pinctrl-0 = <&pinctrl_i2c2>;
>>  	status = "okay";
>> @@ -376,7 +376,7 @@
>>  };
>>  
>>  &i2c4 {
>> -	clock-frequency = <400000>;
>> +	clock-frequency = <100000>;
>>  	pinctrl-names = "default";
>>  	pinctrl-0 = <&pinctrl_i2c4>;
>>  	status = "okay";
> 
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