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bus speed of /dev/i2c-2 on imx6q

Former Member

Hello everyone,

I am unaware as to who sets clock speed on the i2c bus and specifically on the /dev/i2c-2 which is exposed on the board so as to drive external equipment.

I am looking into the linux-boundary kernel files in yocto (dylan) build dir, but I cannot figure out where that is set.

To be honest I don't even know if i'll find that info there, but it seems like the right place to start (after googling about it of course).

 

So who determined the speed (standard mode, fast mode, etc) for the external i2c? if it is a driver , which one should I be looking for?

 

The reason is I am trying to drive some TMC222 low-power stepper motor control ICs, but they do not respond.

Note I have successfully connected a number of other i2c ICs (among others the pca9505x).

 

An answer is not necessary. Any pointers as to how to go about it , so I can learn about this is more than welcome.

Thank you for your help.

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  • look for IMX_I2C_BIT_RATE in drivers/i2c/busses/i2c-imx.c

     

    how it's set depends a lot on the driver is written and on how new/old the kernel is, for example look at arch/arm/mach-davinci/board-da830-evm.c and you'll find

     

    static struct davinci_i2c_platform_data da830_evm_i2c_0_pdata = {

            .bus_freq       = 100,  /* kHz */

            .bus_delay      = 0,    /* usec */

    };

     

    so the speed is set in platform code and the driver takes it from there.

     

    on a newer kernel you may be using devicetree and the i2c speed would be set there rather than platform code. example on BeagleBone Black

    in arch/arm/boot/dts/am335x-bone.dts

     

    &i2c1 {

           status = "okay";

           clock-frequency = <400000>;

     

    other drivers may even have a module parameter you can set when you load the module.

     

    In summary, there are many different ways it can be done image

  • in reply to Former Member

    hello ,

    can you describe pls, how / what is the mechanism  modify it when using module parameter when loading the module.

    thank you

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