T4240QDS PCIe x8 configuration

[vigneshwarensan]

We are working on T4240QDS rev 1 machine.

The current SerDes configuration that we are using is

SerDes protocol 1: 1

SerDes protocol 2: 28

SerDes protocol 3: 6

SerDes protocol 4: 12

To configure the PCI as an x8 slot we chose the values

(SRDS_PRTCL_S3 = 2 and SRDS_PRTCL_S4 = 4).

The inserted card was then booted, the kernel logs showed that the slot was still detected as a x4 slot.

Portion of the Logs:

(PCI Express:5.0GT/s:Width x4) 00:1b:21:ba:9f:6e

MAC: 2, PHY: 15, SFP+: 6, PBA No: Unknown

PCI-Express bandwidth available for this card is not sufficient for optimal performance.

For optimal performance a x8 PCI-Express slot is required

How do I configure the slot (Slot 7) as a x8 slot?

[lunminliang · Accepted solution]

See the table in T4240QDSRM.pdf, your configuration SRDS_PRTCL_S4 = 4 is S4 lane ABCD for PCIe3 and EFGH for PCIe4. According to the table, this routes to SLOT7(0:3) and SLOT8(0:3)

So I think you could try the first one SD4 routes to SLOT7(0:7). To do this, Serdes protocol needs to be changed and BSM4 needs to be set (SW9[2:3]) as below.

[vigneshwarensan]

Thanks. It worked :smileyhappy: