Re: [PATCH net v2] r8169: don't enable chip LTR when the platform has not enabled LTR

On 11.09.2026 15:00, Yogesh Gaur wrote:

On Fri, Sep 11, 2026 at 1:03 AM Heiner Kallweit [off-list ref] wrote:

quoted

On 10.09.2026 15:01, Yogesh Gaur wrote:

quoted

rtl_enable_ltr() programs the MAC to generate LTR messages - ALDPS_LTR_EN,

Empty lines, mail formatting issue?

Yes, I would correct it in v3.

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quoted

LTR_SNOOP_EN, LTR_OBFF_LOCK_EN, plus LINK_SPEED_CHANGE_EN on

RTL8125/RTL8126/RTL8127 - and rtl_hw_aspm_clkreq_enable() calls it on

every ASPM enable, then goes on to let the chip trigger L1.2.



The only gate is tp->aspm_manageable, which records that the OS is allowed

to control ASPM. It says nothing about LTR. LTR is a separate PCIe

capability that only works if every device on the path to the root port

supports it. The PCI core works that out in pci_configure_ltr() and

records the result in pci_dev->ltr_path; per PCIe r6.0 sec 7.5.3.16 a

function must not issue LTR messages while LTR Mechanism Enable is clear.



So on a platform whose hierarchy has no LTR path, the driver tells the

chip to start sending LTR messages nothing will honour, and ties ALDPS -

the PHY's link-down power saving - to them. A report against RTL8125B

(rev 05, firmware rtl8125b-2_0.0.2) in a mini PC shows the effect: 291

Did you verify that this is caused by LTR messages, and not by any other
root cause?

quoted

link down/up transitions in one eight-hour boot, with repeated downshifts

to 100Mbps, against four transitions at boot and then a stable link on

the kernel before the LTR change.



Gate the chip's LTR programming on pci_dev->ltr_path. That field lives

inside CONFIG_PCIEASPM, and without ASPM support there is nothing here to

enable LTR for, so compile the function out in that configuration.



Note this does change CONFIG_PCIEASPM=n builds, which used to program

chip LTR unconditionally: pci_disable_link_state() is a stub that returns

success there, so tp->aspm_manageable ends up set. The PCI core does not

configure LTR in that configuration either.



Fixes: 9ab94a32af70 ("r8169: enable LTR support")

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2529752

Did you verify that your patch fixes the reported issue? Or do you
just assume this? Because in the bug comment history I don't see
a statement that issue has been resolved.

I don't have a board with me, hence have not verified it. I did a
compile check only.

If it's not verified that your patch fixes the reported issue, better
remove the Closes line.

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Assisted-by: LLM

Signed-off-by: Yogesh Gaur <yogeshgaur.83@gmail.com>

---

v2:

 - Gate on pci_dev->ltr_path instead of reading PCI_EXP_DEVCTL2 directly,

   and compile rtl_enable_ltr() out for CONFIG_PCIEASPM=n, where that

   field does not exist and there is nothing to enable LTR for.

   Suggested by Heiner Kallweit.

 - Commit message notes the resulting change for CONFIG_PCIEASPM=n builds.

 - No change to the RTL8125 register programming itself.



v1: https://lore.kernel.org/all/20260909110554.1977-1-yogeshgaur.83@gmail.com/ (local)



 drivers/net/ethernet/realtek/r8169_main.c | 13 +++++++++++++

 1 file changed, 13 insertions(+)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c

index ec4fc21fa21f..05f7a44aff01 100644

--- a/drivers/net/ethernet/realtek/r8169_main.c

+++ b/drivers/net/ethernet/realtek/r8169_main.c

@@ -3035,8 +3035,16 @@ static void rtl_disable_exit_l1(struct rtl8169_private *tp)

      }

 }



+#ifdef CONFIG_PCIEASPM

 static void rtl_enable_ltr(struct rtl8169_private *tp)

 {

+     /* The chip must not issue LTR messages unless LTR is enabled on the

+      * whole path up to the root port. pci_configure_ltr() works that out

+      * and records the result in pci_dev->ltr_path.

+      */

+     if (!tp->pci_dev->ltr_path)

Simpler would be:
if (!IS_ENABLED(CONFIG_PCIEASPM) || !tp->pci_dev->ltr_path)

I tried that and it does not build, because ltr_path itself is declared
inside the #ifdef:

  include/linux/pci.h:443
    #ifdef CONFIG_PCIEASPM
            struct pcie_link_state  *link_state;
            unsigned int    aspm_l0s_support:1;
            unsigned int    aspm_l1_support:1;
            unsigned int    ltr_path:1;
    #endif

IS_ENABLED() is a C expression, so the member reference still has to
compile even when the left operand is 0:

  drivers/net/ethernet/realtek/r8169_main.c: In function 'rtl_enable_ltr':
  error: 'struct pci_dev' has no member named 'ltr_path'
       if (!IS_ENABLED(CONFIG_PCIEASPM) || !tp->pci_dev->ltr_path)

Right, ofc ..

quoted

Then you don't need the stub function.

You are right that the stub function should go, though. v3 drops it and
keeps a single rtl_enable_ltr() with the guard inline:

        static void rtl_enable_ltr(struct rtl8169_private *tp)
        {
                /* comment */
        #ifdef CONFIG_PCIEASPM
                if (!tp->pci_dev->ltr_path)
                        return;
        #else
                return;
        #endif

LGTM

quoted

quoted

+             return;

+

      switch (tp->mac_version) {

      case RTL_GIGA_MAC_VER_80:

              r8168_mac_ocp_write(tp, 0xcdd0, 0x9003);

@@ -3120,6 +3128,11 @@ static void rtl_enable_ltr(struct rtl8169_private *tp)

      /* chip can trigger LTR */

      r8168_mac_ocp_modify(tp, LTR_OBFF_LOCK, 0x0003, LTR_OBFF_LOCK_EN);

 }

+#else

+static void rtl_enable_ltr(struct rtl8169_private *tp)

+{

+}

+#endif



 static void rtl_hw_aspm_clkreq_enable(struct rtl8169_private *tp, bool enable)

 {