Public bug reported:

[Impact]
Dell systems with Realtek 1G Ethernet module fail to enter suspend.

The failure is tied to the RTL8116AF SerDes path. The device cannot report
link readiness through the normal PHY registers. It also keeps hidden PCI
functions active, so the platform cannot enter s0idle and package C10.

[Fix]
Revert the older single r8169 SerDes workaround, then apply the newer
Realtek patch series.

The series:
- net: phy: realtek: add support for dummy phy
- r8169: move funcitons forward
- r8169: fix RTL8116af readiness bug
- r8169: add ltr support for RTL8116af
- r8169: fix RTL8116af can not enter s0idle and c10

A final Ubuntu SAUCE patch gates the RTL8116AF behavior behind a narrow DMI
quirk. The quirk requires both RTL8116AF hardware detection and a Dell
platform DMI match. This avoids changing behavior on other
RTL_GIGA_MAC_VER_52 systems.

https://lore.kernel.org/lkml/[email protected]/

The new series which includes thousand lines of code change is still under
discussion. This size of patches is far beyond the SRU policy and hard to
build a DMI quirk, so we use the old series as a workaround for now.
https://lore.kernel.org/netdev/[email protected]/

[Test Plan]
1. Boot the affected Dell Pro 5 Micro P5M1260 system with the Realtek 1G
   Ethernet module installed.
2. Start a suspend test:
   sudo fwts s3 --s3-multiple=30 --s3-sleep-delay=30

3. Check the result after each resume:
   sudo cat 
/sys/kernel/debug/pmc_core/{package_cstate_show,slp_s0_residency_usec}

Without the patches, the Package C10 and S0idle residency are 0.

With the patches, the Package C10 and S0idle residency are non-zero.

[Where problems could occur]
The risk is in the r8169 Realtek Ethernet driver power-management path.

If the dummy PHY or SerDes link handling is wrong, Ethernet link state may be
reported incorrectly. The interface may fail to come up or may report the
wrong speed after boot or resume.

If the LTR, ASPM, or hidden-function power writes are wrong, suspend may still
fail. The device could also fail to wake or lose network link after resume.

The risky paths are gated by both hardware detection and Dell DMI matching.
Other platforms should keep the old r8169 behavior.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: linux (Ubuntu Resolute)
     Importance: Undecided
     Assignee: AceLan Kao (acelankao)
         Status: In Progress

** Also affects: linux (Ubuntu Resolute)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Resolute)
       Status: New => In Progress

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https://bugs.launchpad.net/bugs/2159004

Title:
  Dell systems fail to enter suspend with Realtek 1G Ethernet module

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