How to use I2C0 via LVDS0 on iMX8?

[sig0912]

Hi community!

I'm trying to use the I2C0 via the LVDS0 block to configure a serializer. I don't understand why the i2c0_lvds0 node is not defined in the file imx8qm-ss-lvds.dtsi.

Only i2c1_lvds0 is there:

i2c1_lvds0: i2c@56247000 {
  compatible = "fsl,imx8qm-lpi2c", "fsl,imx7ulp-lpi2c";
  reg = <0x56247000 0x4000>;
  interrupts = <9>;
  interrupt-parent = <&irqsteer_lvds0>;
  clocks = <&lvds0_i2c0_lpcg 0>,
  <&lvds0_i2c0_lpcg 1>;
  clock-names = "per", "ipg";
  assigned-clocks = <&clk IMX_SC_R_LVDS_0_I2C_0 IMX_SC_PM_CLK_PER>;
  assigned-clock-rates = <24000000>;
  power-domains = <&pd IMX_SC_R_LVDS_0_I2C_0>;
  status = "disabled";
};

So in my custom dts I added the node for the i2c0_lvds0:

&lvds1_subsys {
  i2c0_lvds0: i2c@56246000 {
    compatible = "fsl,imx8qm-lpi2c", "fsl,imx7ulp-lpi2c";
    reg = <0x56246000 0x4000>;
    interrupts = <8>;
    interrupt-parent = <&irqsteer_lvds0>;
    clocks = <&lvds0_i2c0_lpcg 0>,
    <&lvds0_i2c0_lpcg 1>;
    clock-names = "per", "ipg";
    assigned-clocks = <&clk IMX_SC_R_LVDS_0_I2C_0 IMX_SC_PM_CLK_PER>;
    assigned-clock-rates = <24000000>;
    power-domains = <&pd IMX_SC_R_LVDS_0_I2C_0>;
    status = "okay";
  };
};

&i2c0_lvds0 {
  #address-cells = <1>;
  #size-cells = <0>;
  pinctrl-names = "default";
  pinctrl-0 = <&pinctrl_lvds0_lpi2c0>;
  clock-frequency = <400000>;
  status = "okay";

  lvds-panel@1a {
    compatible = "ti,ds90ub947";
    reg = <0x1a>;
    #address-cells = <0x1>;
    #size-cells = <0x0>;
    #reset-cells = <0x1>;
    dual-pixel-mode;

    port {
      ds90ub947_0_in: endpoint {
        clock-lanes = <3>;
        data-lanes = <0 1 2 4>;
        remote-endpoint = <&lvds0_out>;
       };
    };

    display-timings {
      1920X1080P@1a {
        clock-frequency = <72800000>;
        hactive = <1920>;
        vactive = <1080>;
        hfront-porch = <0>;
        hback-porch = <120>;
        hsync-len = <0>;
        vback-porch = <44>;
        vfront-porch = <0>;
        vsync-len = <0>;
        hsync-active = <1>;
        vsync-active = <0>;
      };
    };
  };
};

pinctrl_lvds0_lpi2c0: lvds0lpi2c0grp {
  fsl,pins = <
    IMX8QM_LVDS0_I2C0_SCL_LVDS0_I2C0_SCL 0xc600000c
    IMX8QM_LVDS0_I2C0_SDA_LVDS0_I2C0_SDA 0xc600000c
  >;
};

It's strange that I have to add the i2c0_lvds0 and pinctrl_lvds0_lpi2c0... 

After flashing the new build it seems I can detect that i2c which is listed as i2c-4:

Unfortunately nothing is detected on that i2c

I posted a comment on this post as well where other people seem to have the same problem years ago but they didn't get a clear answer. https://community.nxp.com/t5/i-MX-Processors/IMX8QM-cross-connection-of-the-clock-signals-of-i2c-lvd...

So here are my questions:
1 - Why the i2c0_ldvs0 node is not defined in the file imx8qm-ss-lvds.dtsi?
2 - Will it have any negative consequences by adding that i2c0_ldvs0 node in my own dts?
3 - Do I need to add a configuration in the SCU firmware to get a proper i2c0_lvds0 configuration?
4 - How can I detect that i2c0 from u-boot?
5 - I'm using boot mode flex spi, I don't use M4 cores. Is there any changes to be made on the M4 cores?

Thank you in advance.

Best Regards,
Ingrid

[AldoG · Accepted solution]

Hello,

1 > Do not know which kernel version are you using as reference, but in latest release it is actually there:

https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8qm-ss-lv...

2 > same as above

3 > No, we use one of the pads (IMX8QM_LVDS0_I2C0_SDA_LSIO_GPIO1_IO07)for MIPI DSI:

https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8qm-mek-d...

So, please check that you don’t have this pad muxed to another peripheral.

4 > You may enable it in dts

5 > No it should be ok

Regarding your test, have you tried connecting an oscilloscope or a logic analyzer to check the signals?

Best regards,
Aldo.

[sig0912]

Hi Aldo,

Thank you for your answer!
I'm using kernel 5.4, in this version the i2c0_lvds1 is not there.
It's now working, the problem was I you said the I2C0_SCL pad was defined for the mipi!

So in my case I removed the following node:
pinctrl_mipi0_lpi2c0: mipi0_lpi2c0grp {
  fsl,pins = <
    IMX8QM_MIPI_DSI0_I2C0_SCL_MIPI_DSI0_I2C0_SCL 0xc6000020
    IMX8QM_MIPI_DSI0_I2C0_SDA_MIPI_DSI0_I2C0_SDA 0xc6000020
    IMX8QM_MIPI_DSI0_GPIO0_01_LSIO_GPIO1_IO19 0x00000020
    >;
};

Best Regards,
Ingrid