Adjust LVDS drive strength and slew rate in Apalis TK1

Technical Support
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1

Hi,

we have an LVDS display which is working correctly, but the system is not passing EMC tests because of the signals on the LVDS cable.
According to this article:

it should be possible to adjust drive strength and slew rate on the Apalis TK1.

The informations I’ve collected until now are that:

  1. tegra124-pinctrl driver is responsible of control pin configuration (pinctrl-tegra124.c « pinctrl « drivers - linux-toradex.git - Linux kernel for Apalis, Colibri and Verdin modules)
  2. according to Apalis TK1 datasheet (page 26) LVDS signals are in the avdd_lvds0_io power block
  3. it’s possible to adjust drive strength and slew rate in device tree like this: tegra124-apalis-pinmux.dtsi « tegra124-platforms « dts « boot « arm « arch - linux-toradex.git - Linux kernel for Apalis, Colibri and Verdin modules

The thing that’s not clear to me is which pin group I should drive to adjust lvds signals. If you could tell me which one I should use in nvidia,pins = "drive_xxx"; and explain how to correctly deduct it for the future, it would be very useful.

Thank you,
Diego

2

There is no way to modify LVDS transmitter driver current from the device tree.
You’ll have to modify drivers/video/tegra/dc/sor.c file. In the function tegra_dc_sor_enable_lvds you’ll find writes to NV_SOR_LANE_DRIVE_CURRENT and NV_SOR_LANE4_DRIVE_CURRENT registers.
You can find register definition in the “Tegra K1 Reference Manual”.

3

Thanks, this is the correct answer. For those wondering, details about the registers are at page 1919 of Tegra K1 Mobile Processor Technical Reference Manual.

1 Like
4

You are welcome. Thanks for the information.