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Subject[PATCH 4.9 051/191] PCI/PTM: Inherit Switch Downstream Port PTM settings from Upstream Port
Date
From: Bjorn Helgaas <bhelgaas@google.com>

[ Upstream commit 7b38fd9760f51cc83d80eed2cfbde8b5ead9e93a ]

Except for Endpoints, we enable PTM at enumeration-time. Previously we did
not account for the fact that Switch Downstream Ports are not permitted to
have a PTM capability; their PTM behavior is controlled by the Upstream
Port (PCIe r5.0, sec 7.9.16). Since Downstream Ports don't have a PTM
capability, we did not mark them as "ptm_enabled", which meant that
pci_enable_ptm() on an Endpoint failed because there was no PTM path to it.

Mark Downstream Ports as "ptm_enabled" if their Upstream Port has PTM
enabled.

Fixes: eec097d43100 ("PCI: Add pci_enable_ptm() for drivers to enable PTM on endpoints")
Reported-by: Aditya Paluri <Venkata.AdityaPaluri@synopsys.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/pci/pcie/ptm.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
index 3008bba360f35..ec6f6213960b4 100644
--- a/drivers/pci/pcie/ptm.c
+++ b/drivers/pci/pcie/ptm.c
@@ -47,10 +47,6 @@ void pci_ptm_init(struct pci_dev *dev)
if (!pci_is_pcie(dev))
return;

- pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
- if (!pos)
- return;
-
/*
* Enable PTM only on interior devices (root ports, switch ports,
* etc.) on the assumption that it causes no link traffic until an
@@ -60,6 +56,23 @@ void pci_ptm_init(struct pci_dev *dev)
pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END))
return;

+ /*
+ * Switch Downstream Ports are not permitted to have a PTM
+ * capability; their PTM behavior is controlled by the Upstream
+ * Port (PCIe r5.0, sec 7.9.16).
+ */
+ ups = pci_upstream_bridge(dev);
+ if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM &&
+ ups && ups->ptm_enabled) {
+ dev->ptm_granularity = ups->ptm_granularity;
+ dev->ptm_enabled = 1;
+ return;
+ }
+
+ pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
+ if (!pos)
+ return;
+
pci_read_config_dword(dev, pos + PCI_PTM_CAP, &cap);
local_clock = (cap & PCI_PTM_GRANULARITY_MASK) >> 8;

@@ -69,7 +82,6 @@ void pci_ptm_init(struct pci_dev *dev)
* the spec recommendation (PCIe r3.1, sec 7.32.3), select the
* furthest upstream Time Source as the PTM Root.
*/
- ups = pci_upstream_bridge(dev);
if (ups && ups->ptm_enabled) {
ctrl = PCI_PTM_CTRL_ENABLE;
if (ups->ptm_granularity == 0)
--
2.25.1
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