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PCI-E Link Speed in Linux
My Alchemist 770 GPU supports PCI-E Gen4 x16, but `lspci`` reports it as a Gen1 x1 device:
$ sudo lspci -vvv -s 03:00.0 | grep LnkCap:
LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s L1, Exit Latency L0s <64ns, L1 <1us
However, the full link width and speed is reported by the PCI bridge:
$ sudo lspci -vvv -s 01:00.0 | grep LnkCap:
LnkCap: Port #0, Speed 16GT/s, Width x16, ASPM L1, Exit Latency L1 <64us
The ID of the bridge to which the GPU is connected can be found by examining the PCI-E topology:
$ sudo lspci -vvnn -t
-[0000:00]-+-00.0 Intel Corporation Device [8086:4660]
+-01.0-[01-04]----00.0-[02-04]--+-01.0-[03]----00.0 Intel Corporation Device [8086:56a0]
| \-04.0-[04]----00.0 Intel Corporation Device [8086:4f90]
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