PCIe RX channels configure as short channel

Hello team,

I am really apricated with your support on my previous threads. I have one query in PCIe interface. I am using the Jetson XAVIER NX based custom device. We had connected the PCIe switch with x4 lane connector (pcie@141a0000). I need to do some changes in driver and/or device tree for setting RX channel as a short channel.

Please help me to set the RX channel configurations as a short channel, and suggest us where we need to do change in source code.

Thanks and regards

Hi,

This snippet doesn’t look like from PCIe spec. I see it mention switchtec, is it your endpoint datasheet?

Thanks,
Manikanta

Hello Manikanta,

Thanks for the response. Its our endpoint datasheet.

Is it possible to configure NVIDIA jetson NX SOM(root complex) as a short channel?

Thanks and regards

Hi,

I don’t find such setting part of configuration space. Could you point me to PCIe spec defined config register name?

Thanks,
Manikanta

Hello Manikanta,

Thanks for the quick response.

PCIE Tx/Rx setting for Short Channel is not a standard setting. This settings are provided by our PCIe switch manufacture to optimize the performance of SerDes interface for very short channels.

We would like to know If there is a such type of configuration settings available in Nvidia SOM or not.

If yes, please let us know how to configure it in Nvidia SOM.

Thanks and regards

Hi,

Is the requirement here power savings on a platform with shorter channel ?

We didn’t verified this but you can try PCIe spec defined Tx margin to control the Tx amplitude(half swing/reduced swing settings).

Register: RC_PF0_PCIE_CAP_LINK_CONTROL2_LINK_STATUS2_REG_0
Field: PCIE_CAP_TX_MARGIN

You can refer to Tegra TRM and PCIe spec to understand the settings.

After setting PCIE_CAP_TX_MARGIN, you have retrain the link by setting link retrain.
Register: RC_PF0_PCIE_CAP_LINK_CONTROL_LINK_STATUS_REG_0
Field: PCIE_CAP_RETRAIN_LINK

Use setpci to apply these settings.

Thanks,
Manikanta

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