[PATCH 6.12.y] PCI: Skip Target Speed quirk on clamped ports with no link

[Andreas Wild <andiwild@gmail.com>]

From: "Maciej W. Rozycki" <macro@orcam.me.uk>

Since commit 72780f796468 ("PCI: Always lift 2.5GT/s restriction in PCIe
failed link retraining") the Target Speed quirk lifts a firmware-imposed
2.5GT/s restriction on any downstream port, without checking whether the
link is up.  Where nothing is plugged in, the retraining that follows can
never complete, so each attempt costs PCIE_LINK_RETRAIN_TIMEOUT_MS.  The
quirk makes two of them -- the initial one and the restore on the error
path -- adding a fixed 2 s to every boot.

On an MSI PRO Z690-A WIFI DDR4 (Intel 600 Series PCH) with one empty x1
slot, running v7.2-rc5:

  0.541 pci 0000:00:1c.0: removing 2.5GT/s downstream link speed restriction
  1.541 pci 0000:00:1c.0: retraining failed
  2.541 pci 0000:00:1c.2: [8086:7aba] type 01 class 0x060400

Where the Link Speed has already been clamped at 2.5GT/s and no link has
been established there is nothing worth doing, which is what the kerneldoc
for the quirk already describes: the restriction is to be lifted where
firmware arranged it "and the port reports its link already being up".
Bail out early in that case, before either the ASM2824 workaround or the
removal of the restriction is considered.

Ports whose link is up are unaffected, and so is the ASM2824 workaround,
which is reached with the Target Link Speed not clamped.

With this applied the quirk returns without touching the port: both
messages are gone, enumeration proceeds from 0000:00:1c.0 to 0000:00:1c.2
in 1 ms rather than 2 s, and the systemd "kernel" boot phase goes from
3.011 s to 1.036 s.

Fixes: 72780f796468 ("PCI: Always lift 2.5GT/s restriction in PCIe failed link retraining")
Reported-by: Andreas Wild <andiwild@gmail.com>
Closes: https://lore.kernel.org/lkml/20260801092152.5643-1-andiwild@gmail.com/
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221801
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Andreas Wild <andiwild@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Andreas Wild <andiwild@gmail.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260801201244.4421-1-andiwild@gmail.com
(cherry picked from commit ff8a969f7dc8e79ea6113abcfa983e070b2b585a)
[ Andreas: this tree predates pcie_lbms_seen() and pcie_set_target_speed()
  and still tests LBMS and DLLLA in one expression, so the hunk did not
  apply.  Split that test the same way as upstream and compare the
  LNKCTL2 Target Link Speed field against PCI_EXP_LNKCTL2_TLS_2_5GT
  directly, as the existing code further down already does. ]
Signed-off-by: Andreas Wild <andiwild@gmail.com>
---

Notes:
    Boot-tested on v6.12.116 on the MSI PRO Z690-A WIFI DDR4 from the report (empty
    x1 slot at 0000:00:1c.0), cold boots: without this patch both messages appear
    and enumeration from 00:1c.0 to 00:1c.2 takes 2.001 s; with it neither message
    appears, the step takes 0.001 s, and the systemd "kernel" phase drops from
    3.097 s to 1.098 s.  The other 22 PCI devices enumerate as before.

 drivers/pci/quirks.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index ac9851e3d..a7e2026b1 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -93,8 +93,12 @@ int pcie_failed_link_retrain(struct pci_dev *dev)
 	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &lnkctl2);
 	pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
 	oldlnkctl2 = lnkctl2;
-	if ((lnksta & (PCI_EXP_LNKSTA_LBMS | PCI_EXP_LNKSTA_DLLLA)) ==
-	    PCI_EXP_LNKSTA_LBMS) {
+	if (lnksta & PCI_EXP_LNKSTA_DLLLA) {
+		;
+	} else if ((lnkctl2 & PCI_EXP_LNKCTL2_TLS) ==
+		   PCI_EXP_LNKCTL2_TLS_2_5GT) {
+		return ret;
+	} else if (lnksta & PCI_EXP_LNKSTA_LBMS) {
 		pci_info(dev, "broken device, retraining non-functional downstream link at 2.5GT/s\n");
 
 		lnkctl2 &= ~PCI_EXP_LNKCTL2_TLS;
-- 
2.56.0