PCIe lane reversal on C0

[lunarking1028]

Hi,

We are designing our carrier board for agx-xavier. We would like to reverse PCIe lanes for C0 used for M.2 M key for SSD, in order to facilitate PCB layout. And we use PCIe in root-complex mode ONLY on Xavier side.

Original: UPHY2 → lane0, UPHY3 → lane1, UPHY4 → lane2, UPHY5 → lane3.
Reverse: UPHY5 → lane0, UPHY4 → lane1, UPHY3 → lane2, UPHY2 → lane3.

Please check my attached screenshot for detail.

1. Is this PCIe lane reversal supported by PCIe controller on Xavier?
2. Do I need any software change in Linux device-treee and/or Linux PCIe driver?
3. Can I do the lane reversal on other multi-lane PCIe controllers: C4 and C5?
4. Is this PCIe lane reversal independent on the PCIe endpoint/device that is connected with (work for any PCIe endpoint/device)?
5. Instead of lane reversal, can I do any lane swap in random way within the PCIe controller group? For example, for my C0 case, can I do UPHY3 → lane0, and UPHY2 → lane1 (UPHY4 and PUHY5 unchanged.)? I think the answer is no, but I want to confirm on it.

Regards.

[lunarking1028]

Hi,

Any update on this question? This is kind of urgent which is causing issue for our PCB layout.

Regards

[lunarking1028]

Hi Nvidia,

I also want to confirm on PCIe Polarity Inversion is supported on Xavier. So, please confirm both “Lane Reversal” and “Polarity Inversion”.

I can find a similar post, but that is for NX. I want confirm on Xavier as well.

Does jetson NX module support the pciE lane polarity reversal feature?

if yes - how to set it ? why? - “want to compress the streams and send them to M.2 pci-e” - from dev “we need to flip the lanes to connect it to a different module” “How do we do the lane flipping” For AGX there is such thing as reverese polarity support: PCIe controller configurations: x8 lane co``` The Jetson Xavier NX module integrates two PCIe controllers supporting: • Connections to two interfaces (1x1 + 1x4). • x1 (supports Root Port only), x4 (supports Root Port or Endpoint modes) U…

Regards.

[omp]

Lane reversal support for of AGX and NX is same.

Does jetson NX module support the pciE lane polarity reversal feature?

Hi, I am assuming this question is for M.2 Key M slot, because Key E supports only one lane and there is no concept of lane reversal, Jetson NX M.2 Key M slot supports both lane reversal and polarity reversal. Hardware takes care of it, no need for extra software programming. However there is one limitation, lane reversal fails if we want to get the link up in x1. If you are using complete x4, then lane reversal works without any issue. Thanks, Manikanta

[lunarking1028]

Hi

Thanks for you reply.
Can you confirm on both “Lane Reversal” and “Polarity Inversion”? (not just lane reversal)

Thanks.

[omp]

Yes, Xavier supports both.