i.MX8M Plus PCIe link regression

[Tim Harvey]

On Tue, Mar 3, 2026 at 4:38 AM Alexander Stein
<alexander.stein at ew.tq-group.com> wrote:
>
> Hi,
>
> these days I noticed that there is a PCIe link regression on my i.MX8MP
> platform (TQMa8MPxL) running next-20260227.
> I could bisect it back to commit 9c03e30e3ade3 ("PCI: imx6: Skip link up
> workaround for newer platforms"). I always get the following errors:
>
> imx6q-pcie 33800000.pcie: Link failed to come up. LTSSM: CFG_LINKWD_START
> imx6q-pcie 33800000.pcie: probe with driver imx6q-pcie failed with error -110
>
> Connected is a Gen1 PCIe -> Ethernet adapter. Interestingly a Gen2 device is
> detected without issues.
>
> Reverting 3c96a61dd2e098dda8dcac3dce3d38a3c87afbfc and
> b9a8d28ebbf118bb3eac953f4a37abbd341257ab "fixes" my platform, both Gen 1 and
> Gen 2 devices are detect. Commit 3c96a61dd2e098dda8dcac3dce3d38a3c87afbfc is only
> required for conflict free revert.
>
> Here is a summary with outputs:
> Gen 1 device
> > 00:00.0 PCI bridge: Synopsys, Inc. DWC_usb3 / PCIe bridge (rev 01)
> > 01:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
> > RTL8111/8168/8211/8411 PCI Express Gigabit Ethernet Controller (rev 01)
>
> Gen 2 device
> > 00:00.0 PCI bridge: Synopsys, Inc. DWC_usb3 / PCIe bridge (rev 01)
> > 01:00.0 SATA controller: Marvell Technology Group Ltd. 88SE9128 PCIe SATA 6
> > Gb/s RAID controller (rev 20)
>
> output of "dmesg | grep imx6q-pcie". Common part for all tests:
> > imx6q-pcie 33800000.pcie: host bridge /soc at 0/pcie at 33800000 ranges:
> > imx6q-pcie 33800000.pcie:       IO 0x001ff80000..0x001ff8ffff ->
> > 0x0000000000
> > imx6q-pcie 33800000.pcie:      MEM 0x0018000000..0x001fefffff ->
> > 0x0018000000
> > imx6q-pcie 33800000.pcie: config reg[1] 0x1ff00000 == cpu 0x1ff00000
> > imx6q-pcie 33800000.pcie: iATU: unroll T, 4 ob, 4 ib, align 64K, limit 16G
>
> next-20260227
> Gen 1
> > imx6q-pcie 33800000.pcie: Link failed to come up. LTSSM: CFG_LINKWD_START
> > imx6q-pcie 33800000.pcie: probe with driver imx6q-pcie failed with error -110
>
> Gen 2
> > imx6q-pcie 33800000.pcie: PCIe Gen.2 x1 link up
> > imx6q-pcie 33800000.pcie: PCI host bridge to bus 0000:00
>
> next-20260227 + reverts
> Gen 1
> > imx6q-pcie 33800000.pcie: PCIe Gen.1 x1 link up
> > imx6q-pcie 33800000.pcie: PCIe Gen.1 x1 link up
> > imx6q-pcie 33800000.pcie: PCI host bridge to bus 0000:00
>
> Gen 2
> > imx6q-pcie 33800000.pcie: PCIe Gen.1 x1 link up
> > imx6q-pcie 33800000.pcie: PCIe Gen.2 x1 link up
> > imx6q-pcie 33800000.pcie: PCI host bridge to bus 0000:00
>
> What can we do here? I'm wondering why Gen 2 trains correctly, while Gen 1
> doesn't.
>
> Best regards,
> Alexander

Hi Alexander,

Does your link partner perhaps suffer from some errata?

Ironically I have had PCI link issues that required the patch you are
needing to revert on IMX8MP with specific switches.

Best Regards,

Tim