From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: linux-pci@vger.kernel.org
Cc: Bjorn Helgaas <bhelgaas@google.com>,
Lukas Wunner <lukas@wunner.de>,
Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: [PATCH v2] PCI/PTM: Do not enable PTM solely based on the capability existense
Date: Tue, 28 Oct 2025 07:04:27 +0100 [thread overview]
Message-ID: <20251028060427.2163115-1-mika.westerberg@linux.intel.com> (raw)
It is not advisable to enable PTM solely based on the fact that the
capability exists. Instead there are separate bits in the capability
register that need to be set for the feature to be enabled for a given
component (this is suggestion from Intel PCIe folks):
- PCIe Endpoint that has PTM capability must to declare requester
capable
- PCIe Switch Upstream Port that has PTM capability must declare
at least responder capable
- PCIe Root Port must declare root port capable.
Currently we see following:
pci 0000:01:00.0: [8086:5786] type 01 class 0x060400 PCIe Switch Upstream Port
pci 0000:01:00.0: PCI bridge to [bus 00]
pci 0000:01:00.0: bridge window [io 0x0000-0x0fff]
pci 0000:01:00.0: bridge window [mem 0x00000000-0x000fffff]
pci 0000:01:00.0: bridge window [mem 0x00000000-0x000fffff 64bit pref]
...
pci 0000:01:00.0: PTM enabled, 4ns granularity
...
pcieport 0000:00:07.0: AER: Multiple Uncorrectable (Non-Fatal) error message received from 0000:00:07.0
pcieport 0000:00:07.0: PCIe Bus Error: severity=Uncorrectable (Non-Fatal), type=Transaction Layer, (Receiver ID)
pcieport 0000:00:07.0: device [8086:e44e] error status/mask=00200000/00000000
pcieport 0000:00:07.0: [21] ACSViol (First)
The 01:00.0 PCIe Upstream Port has this:
Capabilities: [220 v1] Precision Time Measurement
PTMCap: Requester- Responder- Root-
This happens because Linux sees the PTM capability and blindly enables
PTM which then causes the AER error to trigger.
Fix this by enabling PTM only if the above described criteria is met.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
Previous version can be seen:
https://lore.kernel.org/linux-pci/20251021104833.3729120-1-mika.westerberg@linux.intel.com/
Changes from the previous version:
- Limit Switch Upstream Port only to Responder, not both Requester and
Responder.
drivers/pci/pcie/ptm.c | 31 +++++++++++++++++++++++++++----
1 file changed, 27 insertions(+), 4 deletions(-)
diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
index 65e4b008be00..5ebb2edb4dec 100644
--- a/drivers/pci/pcie/ptm.c
+++ b/drivers/pci/pcie/ptm.c
@@ -81,9 +81,24 @@ void pci_ptm_init(struct pci_dev *dev)
dev->ptm_granularity = 0;
}
- if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
- pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM)
- pci_enable_ptm(dev, NULL);
+ switch (pci_pcie_type(dev)) {
+ case PCI_EXP_TYPE_ROOT_PORT:
+ /*
+ * Root Port must declare Root Capable if we want to
+ * enable PTM for it.
+ */
+ if (dev->ptm_root)
+ pci_enable_ptm(dev, NULL);
+ break;
+ case PCI_EXP_TYPE_UPSTREAM:
+ /*
+ * Switch Upstream Ports must at least declare Responder
+ * Capable if we want to enable PTM for it.
+ */
+ if (cap & PCI_PTM_CAP_RES)
+ pci_enable_ptm(dev, NULL);
+ break;
+ }
}
void pci_save_ptm_state(struct pci_dev *dev)
@@ -125,7 +140,7 @@ static int __pci_enable_ptm(struct pci_dev *dev)
{
u16 ptm = dev->ptm_cap;
struct pci_dev *ups;
- u32 ctrl;
+ u32 cap, ctrl;
if (!ptm)
return -EINVAL;
@@ -144,6 +159,14 @@ static int __pci_enable_ptm(struct pci_dev *dev)
return -EINVAL;
}
+ /*
+ * PCIe Endpoint must declare Requester Capable before we can
+ * enable PTM for it.
+ */
+ pci_read_config_dword(dev, ptm + PCI_PTM_CAP, &cap);
+ if (!(cap & PCI_PTM_CAP_REQ))
+ return -EINVAL;
+
pci_read_config_dword(dev, ptm + PCI_PTM_CTRL, &ctrl);
ctrl |= PCI_PTM_CTRL_ENABLE;
--
2.50.1
next reply other threads:[~2025-10-28 6:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-28 6:04 Mika Westerberg [this message]
2025-10-28 9:53 ` [PATCH v2] PCI/PTM: Do not enable PTM solely based on the capability existense Lukas Wunner
2025-10-28 17:06 ` Bjorn Helgaas
2025-10-29 5:33 ` Mika Westerberg
2025-10-29 10:53 ` Lukas Wunner
2025-10-29 11:20 ` Mika Westerberg
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