How to Carry out DMA transfer when sending data using PCIe from NVIDIA Root Port to a custom end point

[Manikanta]

Hi,

To do DMA transfer, hw should have a DMA engine. Below thread holds good only when you are using Tegra PCIe in EP mode.

DMA to PCIe BARs

Yes. It is not possible to use the General-Purpose DMA engine to do DMA to/from PCIe BAR region. PCIe root port has a DMA engine build into it. Please take a look at the registers mentioned in the TRM (path: High-Speed I/O → PCI Express (PCIe) Controller → PCIe Registers → PCIe IATU) Also, take a look at dma_write() and dma_read() functions in pcie-tegra.c file

PCIe spec doesn’t talk about DMA engine, so industry standards is to have DMA engine as part of EP.

If you are able to do DMA from EP to RP then use same DMA engine to transfer data from Tegra RP to EP using DMA read functionality.

Disabling SMMU is not the solution here and we don’t recommend it. You need to implement DMA programming sequence.

Thanks,
Manikanta