J721EXSOMXEVM: Does TDA4 EP mode support P2P after being configured in EP mode?

Xujie Zhao

Prodigy 50 points

Part Number: J721EXSOMXEVM

Hello,

I would like to implement PCIe P2P functionality using J721E, with one J721E acting as the RC and the other as the EP.

1.Does J721E（EP mode） support P2P?

2.If the J721E does not support PCIe P2P in EP mode, are there any other product series that can achieve this?

3.I am also unclear about the hardware requirements for enabling PCIe P2P in EP mode. Do you have any related documentation on P2P hardware?

Best regards

9 天前

0 Eirwen 9 天前

TI__Genius 10655 points

已经收到了您的案例，调查需要些时间，感谢您的耐心等待。

0 Xujie Zhao 8 天前回复 Eirwen

Prodigy 50 points

Looking forward to your reply.

Best regard

0 Lydia 7 天前回复 Xujie Zhao

TI__Genius 12625 points

Hi,

By P2P, if you mean two EP devices connected to the J721E RC communicating with each other directly with no help from RC, then no PCIe P2P support.

However, the closest to this would be the PCIe backplane Linux demo here in which two RC devices can communicate with each other through a third device that has multiple EP instances: https://software-dl.ti.com/jacinto7/esd/processor-sdk-linux-jacinto7/10_01_00_04/exports/docs/linux/Foundational_Components/Kernel/Kernel_Drivers/PCIe/PCIe_Backplane.html

Can I get more details on what the full set up is?

For example, is it a SSD EP that the J721E EP is trying to access without interference from J721E RC like below. For this, we do not have support for, and customer will have to write some software similar to the PCIe backplane demo, so that the RC kicks off read/writes to the SSD EP based off of J721E EP's requests.

Regards,

Lydia

0 Xujie Zhao 1 天前回复 Lydia

Prodigy 50 points

Thank you for your reply.

I am aware of the TI NTB solution, but it is not very suitable for my project. Therefore, I am considering the P2P approach.

When you say it is not supported, do you mean that the EP does not support it, or the RC does not support it? I understand that P2P requires support from the RC or a PCIe switch. If the RC does not support it, I can consider using a PCIe switch to implement P2P. However, if the EP itself does not support it, could you explain the reason?
The J721E EP has a DMA controller, correct? Does this mean I can modify the destination address (SSD BAR) in the driver to achieve P2P transfers, assuming the RC supports P2P?

In addition, I cannot see the image you sent.

Best regards.

0 Lydia 13 小时前回复 Xujie Zhao

TI__Genius 12625 points

Hi Ying,

J721E RC does not support since each PCIe port/controller comes up as a separate bridge on J721E.

PCIe switch would be an option to have everything under one bridge, but TI does not have any examples for this. Also, J721E in particular has an errata for using PCIe switches which add to the complexity: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1264686/faq-j721exsomxevm-how-to-work-around-errata-i2086-for-pcie-switches-and-multifunction-devices-for-j721e-tda4vm-dra829

And he following Linux kernel documentation clarifies the limitations with P2P that makes it tricky to implement:

https://docs.kernel.org/driver-api/pci/p2pdma.html

As for EP not supporting, this will depend on the EP. For example, I have seen FPGA EP that requires very large 64GB mapped to memory space for P2P transactions. J721E limit for PCIe is 4GB space. This is just one example, but you/customer will have to check the EP's datasheet for this one.

And also share some more details on why this feature is needed, and why the backplane example would not work in the customer's usecase?

Regards,

Lydia

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J721EXSOMXEVM: Does TDA4 EP mode support P2P after being configured in EP mode?