linux-kernel - [PATCH 4.9 051/191] PCI/PTM: Inherit Switch Downstream Port PTM settings from Upstream Port

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Message-Id: <20200629154007.2495120-52-sashal@kernel.org>
Date:   Mon, 29 Jun 2020 11:37:47 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Aditya Paluri <Venkata.AdityaPaluri@...opsys.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 051/191] PCI/PTM: Inherit Switch Downstream Port PTM settings from Upstream Port

From: Bjorn Helgaas <bhelgaas@...gle.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@...opsys.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Signed-off-by: Sasha Levin <sashal@...nel.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