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From:   Vidya Sagar <vidyas@nvidia.com>
To:     <bhelgaas@google.com>
CC:     <linux-pci@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <vsethi@nvidia.com>, <kthota@nvidia.com>, <mmaddireddy@nvidia.com>,
        <vidyas@nvidia.com>, <sagar.tv@gmail.com>
Subject: [PATCH V1] PCI: pciehp: Disable ACS Source Validation during hot-remove
Date:   Wed, 11 Jan 2023 20:22:06 +0530
Message-ID: <20230111145206.23919-1-vidyas@nvidia.com>
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PCIe 6.0, 6.12.1.1 specifies that downstream devices are permitted to
send upstream messages before they have been assigned a bus number and
such messages have a Requester ID with Bus number set to 00h.
If the Downstrem port has ACS Source Validation enabled, these messages
will be detected as ACS violation error.
Hence, disable ACS Source Validation in the bridge device during
hot-remove operation and re-enable it after enumeration of the
downstream hierarchy but before binding the respective device drivers.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
 drivers/pci/hotplug/pciehp_pci.c | 13 ++++++++++++-
 drivers/pci/pci.c                | 20 ++++++++++++++++++++
 include/linux/pci.h              |  6 ++++++
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c
index d17f3bf36f70..ad90bcf3f621 100644
--- a/drivers/pci/hotplug/pciehp_pci.c
+++ b/drivers/pci/hotplug/pciehp_pci.c
@@ -63,6 +63,7 @@ int pciehp_configure_device(struct controller *ctrl)
 
 	pci_assign_unassigned_bridge_resources(bridge);
 	pcie_bus_configure_settings(parent);
+	pci_configure_acs_sv(bridge, true);
 	pci_bus_add_devices(parent);
 
  out:
@@ -117,6 +118,16 @@ void pciehp_unconfigure_device(struct controller *ctrl, bool presence)
 		}
 		pci_dev_put(dev);
 	}
-
+	/*
+	 * PCIe 6.0, 6.12.1.1 specifies that downstream devices are permitted
+	 * to send upstream messages before they have been assigned a bus
+	 * number and such messages have a Requester ID with Bus number
+	 * set to 00h. If the Downstrem port has ACS Source Validation enabled,
+	 * these messages will be detected as ACS violation error.
+	 * Hence, disable ACS Source Validation here and re-enable it after
+	 * enumeration of the downstream hierarchy and before binding the
+	 * respective device drivers in pciehp_configure_device().
+	 */
+	pci_configure_acs_sv(ctrl->pcie->port, false);
 	pci_unlock_rescan_remove();
 }
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 95bc329e74c0..d3d0246fddd9 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -991,6 +991,26 @@ static void pci_enable_acs(struct pci_dev *dev)
 	pci_disable_acs_redir(dev);
 }
 
+void pci_configure_acs_sv(struct pci_dev *dev, bool flag)
+{
+	u16 cap;
+	u16 ctrl;
+
+	if (!pci_acs_enable || !dev->acs_cap)
+		return;
+
+	pci_read_config_word(dev, dev->acs_cap + PCI_ACS_CAP, &cap);
+	pci_read_config_word(dev, dev->acs_cap + PCI_ACS_CTRL, &ctrl);
+
+	if (flag)
+		ctrl |= (cap & PCI_ACS_SV);
+	else
+		ctrl &= ~(cap & PCI_ACS_SV);
+
+	pci_write_config_word(dev, dev->acs_cap + PCI_ACS_CTRL, ctrl);
+}
+EXPORT_SYMBOL_GPL(pci_configure_acs_sv);
+
 /**
  * pci_restore_bars - restore a device's BAR values (e.g. after wake-up)
  * @dev: PCI device to have its BARs restored
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 060af91bafcd..c36ac3eb2843 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -2239,6 +2239,12 @@ void pci_hp_create_module_link(struct pci_slot *pci_slot);
 void pci_hp_remove_module_link(struct pci_slot *pci_slot);
 #endif
 
+#if defined(CONFIG_HOTPLUG_PCI_PCIE)
+void pci_configure_acs_sv(struct pci_dev *dev, bool flag);
+#else
+void pci_configure_acs_sv(struct pci_dev *dev, bool flag) {}
+#endif
+
 /**
  * pci_pcie_cap - get the saved PCIe capability offset
  * @dev: PCI device
-- 
2.17.1