linux-kernel - [RFC] PCI: Fix the issue of link speed downgrade after link retraining

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Message-Id: <20241107143758.12643-1-guojinhui.liam@bytedance.com>
Date: Thu,  7 Nov 2024 22:37:58 +0800
From: Jinhui Guo <guojinhui.liam@...edance.com>
To: bhelgaas@...gle.com,
	macro@...am.me.uk
Cc: linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	guojinhui.liam@...edance.com
Subject: [RFC] PCI: Fix the issue of link speed downgrade after link retraining

The link speed is downgraded to 2.5 GT/s when a Samsung NVMe device
is hotplugged into a Intel PCIe root port [8086:0db0].

```
+-[0000:3c]-+-00.0  Intel Corporation Ice Lake Memory Map/VT-d
|           ...
|           +02.0-[3d]----00.0  Samsung Electronics Co Ltd Device a80e
```

Some printing information can be obtained when the issue emerges.
"Card present" is reported twice via external interrupts due to
a slight tremor when the Samsung NVMe device is plugged in.
The failure of the link activation for the first time leads to
the link speed of the root port being mistakenly downgraded to 2.5G/s.

```
[ 8223.419682] pcieport 0000:3d:02.0: pciehp: Slot(1): Card present
[ 8224.449714] pcieport 0000:3d:02.0: broken device, retraining non-functional downstream link at 2.5GT/s
[ 8225.518723] pcieport 0000:3d:02.0: pciehp: Slot(1): Card present
[ 8225.518726] pcieport 0000:3d:02.0: pciehp: Slot(1): Link up
```

To avoid wrongly setting the link speed to 2.5GT/s, only allow
specific pcie devices to perform link retrain.

Fixes: a89c82249c37 ("PCI: Work around PCIe link training failures")
Signed-off-by: Jinhui Guo <guojinhui.liam@...edance.com>
---
 drivers/pci/quirks.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index dccb60c1d9cc..59858156003b 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -91,7 +91,8 @@ int pcie_failed_link_retrain(struct pci_dev *dev)
 	int ret = -ENOTTY;
 
 	if (!pci_is_pcie(dev) || !pcie_downstream_port(dev) ||
-	    !pcie_cap_has_lnkctl2(dev) || !dev->link_active_reporting)
+	    !pcie_cap_has_lnkctl2(dev) || !dev->link_active_reporting ||
+		!pci_match_id(ids, dev))
 		return ret;
 
 	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &lnkctl2);
@@ -119,8 +120,7 @@ int pcie_failed_link_retrain(struct pci_dev *dev)
 	}
 
 	if ((lnksta & PCI_EXP_LNKSTA_DLLLA) &&
-	    (lnkctl2 & PCI_EXP_LNKCTL2_TLS) == PCI_EXP_LNKCTL2_TLS_2_5GT &&
-	    pci_match_id(ids, dev)) {
+	    (lnkctl2 & PCI_EXP_LNKCTL2_TLS) == PCI_EXP_LNKCTL2_TLS_2_5GT) {
 		u32 lnkcap;
 
 		pci_info(dev, "removing 2.5GT/s downstream link speed restriction\n");
-- 
2.20.1