Bug 195253 - disabling PCIEASPM makes link speed drop from 5 GT/s to 2.5 GT/s
Summary: disabling PCIEASPM makes link speed drop from 5 GT/s to 2.5 GT/s
Status: NEW
Alias: None
Product: Drivers
Classification: Unclassified
Component: PCI (show other bugs)
Hardware: ARM Linux
: P1 normal
Assignee: drivers_pci@kernel-bugs.osdl.org
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2017-04-04 20:21 UTC by Uwe Kleine-König
Modified: 2022-02-17 00:18 UTC (History)
1 user (show)

See Also:
Kernel Version: 4.9
Subsystem:
Regression: No
Bisected commit-id:

Attachments
lspci -vv with PCIEASPM=n (9.82 KB, text/plain)
2017-04-04 20:21 UTC, Uwe Kleine-König 		Details
lspci -vv with PCIEASPM=y (9.81 KB, text/plain)
2017-04-04 20:22 UTC, Uwe Kleine-König 		Details
Add an attachment (proposed patch, testcase, etc.)

Description Uwe Kleine-König 2017-04-04 20:21:46 UTC 
Created attachment 255759 [details]
lspci -vv with PCIEASPM=n

Hello,

on an Armada XP (i.e. arm) system disabling PCIEASPM results in different link speed. See attachments for lspci with and without PCIEASPM.

Best regards
Uwe
Comment 1 Uwe Kleine-König 2017-04-04 20:22:54 UTC 
Created attachment 255761 [details]
lspci -vv with PCIEASPM=y
Comment 2 Pali Rohár 2022-02-17 00:18:40 UTC 
I saw similar syndromes on other Armada SoCs.

It looks like that in this particular cases is link initialized only to 2.5 GT/s and "upgrade" to 5 GT/s is done after explicit link retraining.

As PCIe ASPM during initialization is calling link retraining, it means that it "upgrades" link speed to 5 GT/s.

But there are some cards which do not like link retraining and just crash when kernel do it explicitly. See bug #209833 and bug #192441.

I guess that this is HW issue in Armada PCIe IP.
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