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I'm debugging something of an esoteric driver/BIOS compatibility issue. One possible lead I've found is mentions of possible mismatches of / misdetection of PCI Max Payload Size (MPS). I tried rebooting with pci=pcie_bus_peer2peer on the kernel command line to limit the MPS to 128 bytes on all nodes, but that didn't solve my problem so I'd like to query to make sure it took effect (and to see if anything changes when I remove it again).

What tools could I use, or where in /sys or /proc would I look to find the MPS for each of the PCI devices in the tree to my problem device?

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sudo lspci -vv |grep -P '^\d|Payload'

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  • I see the Max Payload listed under both the DevCap and DevCtl headings. Should I interpret that as the maximum supported vs. the maximum negotiated?
    – Huckle
    Commented Mar 11, 2018 at 4:31
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    yes, that's exactly right. DevCtl is the live setting. Some details here: community.mellanox.com/docs/…
    – Oh My Goodness
    Commented Mar 11, 2018 at 14:31

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