[PATCH v4] PCI/PTM: Enable PTM only if it advertises a role

[Mika Westerberg <mika.westerberg@linux.intel.com>]

We have a Upstream Port (2b:00.0) that has following in the PTM capability:

  Capabilities: [220 v1] Precision Time Measurement
		PTMCap: Requester- Responder- Root-

Linux enables PTM for this without looking into what roles it actually
supports. Immediately after enabling PTM we start getting these:

  pci 0000:2b:00.0: [8086:5786] type 01 class 0x060400 PCIe Switch Upstream Port
  ...
  pci 0000:2b:00.0: PTM enabled, 4ns granularity
  ...
  pcieport 0000:00:07.1: AER: Multiple Uncorrectable (Non-Fatal) error message received from 0000:00:07.1
  pcieport 0000:00:07.1: PCIe Bus Error: severity=Uncorrectable (Non-Fatal), type=Transaction Layer, (Receiver ID)
  pcieport 0000:00:07.1:   device [8086:e44f] error status/mask=00200000/00000000
  pcieport 0000:00:07.1:    [21] ACSViol                (First)
  pcieport 0000:00:07.1: AER:   TLP Header: 0x34000000 0x00000052 0x00000000 0x00000000

Fix this by enabling PTM only if any of the following conditions are
true (see more in PCIe r7.0 sec 6.21.1 figure 6-21):

  - 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.

While there make the enabling happen for all in __pci_enable_ptm() instead
of enabling some in pci_ptm_init() and some in __pci_enable_ptm().

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
Previous versions can be seen:

  v3: https://lore.kernel.org/linux-pci/20251030134606.3782352-1-mika.westerberg@linux.intel.com/
  v2: https://lore.kernel.org/linux-pci/20251028060427.2163115-1-mika.westerberg@linux.intel.com/
  v1: https://lore.kernel.org/linux-pci/20251021104833.3729120-1-mika.westerberg@linux.intel.com/

Changes from v3:

  - Cache the responder and requester capability bits.
  - Enable PTM only in __pci_enable_ptm().
  - Update $subject and commit message.
  - Since this is changed quite a lot, I dropped the Reviewed-by from Lukas
    and also stable tag.

Changes from v2:

  - Limit the check in __pci_enable_ptm() to Endpoints and Legacy
    Endpoints.
  - Added stable tags suggested by Lukas, and PCIe spec reference.
  - Added Reviewed-by tag from Lukas (hope it is okay to keep).

Changes from v1:

  - Limit Switch Upstream Port only to Responder, not both Requester and
    Responder.

 drivers/pci/pcie/ptm.c | 41 ++++++++++++++++++++++++++++++++++++++---
 include/linux/pci.h    |  2 ++
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
index 65e4b008be00..30e25f1ad28e 100644
--- a/drivers/pci/pcie/ptm.c
+++ b/drivers/pci/pcie/ptm.c
@@ -81,9 +81,12 @@ 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);
+	if (cap & PCI_PTM_CAP_RES)
+		dev->ptm_responder = 1;
+	if (cap & PCI_PTM_CAP_REQ)
+		dev->ptm_requester = 1;
+
+	pci_enable_ptm(dev, NULL);
 }
 
 void pci_save_ptm_state(struct pci_dev *dev)
@@ -144,6 +147,38 @@ static int __pci_enable_ptm(struct pci_dev *dev)
 			return -EINVAL;
 	}
 
+	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)
+			return -EINVAL;
+		break;
+	case PCI_EXP_TYPE_UPSTREAM:
+		/*
+		 * Switch Upstream Ports must at least declare Responder
+		 * Capable if we want to enable PTM for it.
+		 */
+		if (!dev->ptm_responder)
+			return -EINVAL;
+		break;
+
+	case PCI_EXP_TYPE_ENDPOINT:
+	case PCI_EXP_TYPE_LEG_END:
+		/*
+		 * PCIe Endpoint must declare Requester Capable before we
+		 * can enable PTM for it.
+		 */
+		if (!dev->ptm_requester)
+			return -EINVAL;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
 	pci_read_config_dword(dev, ptm + PCI_PTM_CTRL, &ctrl);
 
 	ctrl |= PCI_PTM_CTRL_ENABLE;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index d1fdf81fbe1e..d5018cb5c331 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -500,6 +500,8 @@ struct pci_dev {
 #ifdef CONFIG_PCIE_PTM
 	u16		ptm_cap;		/* PTM Capability */
 	unsigned int	ptm_root:1;
+	unsigned int	ptm_responder:1;
+	unsigned int	ptm_requester:1;
 	unsigned int	ptm_enabled:1;
 	u8		ptm_granularity;
 #endif
-- 
2.50.1