i.MX8M Plus PCIe link regression

[Alexander Stein <alexander.stein@ew.tq-group.com>]

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@0/pcie@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
-- 
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Amtsgericht München, HRB 105018
Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
http://www.tq-group.com/