Testado na Beaglebone Black rev. C com Debian 7.5 e 7.7
#tirar o backup do device tree
cp /boot/uboot/dtbs/am335x-boneblack.dtb /boot/uboot/dtbs/am335x-boneblack.dtb-backup
#converte device tree binário para texto
dtc -I dtb -O dts -o /boot/uboot/dtbs/am335x-boneblack.dts /boot/uboot/dtbs/am335x-boneblack.dtb
#editar a clock-frequency para 400000
nano /boot/uboot/dtbs/am335x-boneblack.dts
i2c@4819c000 {
compatible = "ti,omap4-i2c";
#address-cells = <0x1>;
#size-cells = <0x0>;
ti,hwmods = "i2c3";
reg = <0x4819c000 0x1000="">;
interrupts = <0x1e>;
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <0x7>;
#clock-frequency = <0x186a0>; //100KHz
clock-frequency = <400000>;
#converte device tree de texto para binário
dtc -I dts -O dtb -o /boot/uboot/dtbs/am335x-boneblack.dtb /boot/uboot/dtbs/am335x-boneblack.dts
reiniciar, e procure no log, deve estar em 400KHz agora.
[ 0.131766] omap_i2c 44e0b000.i2c: bus 0 rev0.11 at 400 kHz
[ 0.132684] input: tps65217_pwr_but as /devices/ocp.3/44e0b000.i2c/i2c-0/0-0024/input/input0
[ 0.140854] omap_i2c 44e0b000.i2c: unable to select pin group
[ 0.141335] omap_i2c 4819c000.i2c: bus 1 rev0.11 at 400 kHz
Desativar o i2c das CAPES
#converte de binário para texto
dtc -I dtb -O dts -o am335x-boneblack.dts am335x-boneblack.dtb
#mudar de okay para disabled
status = "okay";
status = "disabled";
#converte de texto para binário
dtc -I dts -O dtb -o am335x-boneblack.dtb am335x-boneblack.dts
