[PATCH 6.18 292/752] PCI: Enable ACS after configuring IOMMU for OF platforms

Sasha Levin
2026-02-28T17:52:13Z

From: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>

[ Upstream commit c41e2fb67e26b04d919257875fa954aa5f6e392e ]

Platform, ACPI, or IOMMU drivers call pci_request_acs(), which sets
'pci_acs_enable' to request that ACS be enabled for any devices enumerated
in the future.

OF platforms called pci_enable_acs() for the first device before
of_iommu_configure() called pci_request_acs(), so ACS was never enabled for
that device (typically a Root Port).

Call pci_enable_acs() later, from pci_dma_configure(), after
of_dma_configure() has had a chance to call pci_request_acs().

Here's the call path, showing the move of pci_enable_acs() from
pci_acs_init() to pci_dma_configure(), where it always happens after
pci_request_acs():

pci_device_add
pci_init_capabilities
pci_acs_init
- pci_enable_acs
- if (pci_acs_enable) <-- previous test
- ...
device_add
bus_notify(BUS_NOTIFY_ADD_DEVICE)
iommu_bus_notifier
iommu_probe_device
iommu_init_device
dev->bus->dma_configure
pci_dma_configure # pci_bus_type.dma_configure
of_dma_configure
of_iommu_configure
pci_request_acs
pci_acs_enable = 1 <-- set
+ pci_enable_acs
+ if (pci_acs_enable) <-- new test
+ ...
bus_probe_device
device_initial_probe
...
really_probe
dev->bus->dma_configure
pci_dma_configure # pci_bus_type.dma_configure
...
pci_enable_acs

Note that we will now call pci_enable_acs() twice for every device, first
from the iommu_probe_device() path and again from the really_probe() path.
Presumably that's not an issue since we also call dev->bus->dma_configure()
twice.

For the ACPI platforms, pci_request_acs() is called during ACPI
initialization time itself, independent of the IOMMU framework.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Link: https://patch.msgid.link/20260102-pci_acs-v3-1-72280b94d288@oss.qualcomm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/pci/pci-driver.c | 8 ++++++++
drivers/pci/pci.c | 10 +---------
drivers/pci/pci.h | 1 +
3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 327b21c48614d..b4111c92c9572 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -1652,6 +1652,14 @@ static int pci_dma_configure(struct device *dev)
ret = acpi_dma_configure(dev, acpi_get_dma_attr(adev));
}

+ /*
+ * Attempt to enable ACS regardless of capability because some Root
+ * Ports (e.g. those quirked with *_intel_pch_acs_*) do not have
+ * the standard ACS capability but still support ACS via those
+ * quirks.
+ */
+ pci_enable_acs(to_pci_dev(dev));
+
pci_put_host_bridge_device(bridge);

/* @drv may not be valid when we're called from the IOMMU layer */
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 31d443f819a7c..d147e412668bf 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1015,7 +1015,7 @@ static void pci_std_enable_acs(struct pci_dev *dev, struct pci_acs *caps)
* pci_enable_acs - enable ACS if hardware support it
* @dev: the PCI device
*/
-static void pci_enable_acs(struct pci_dev *dev)
+void pci_enable_acs(struct pci_dev *dev)
{
struct pci_acs caps;
bool enable_acs = false;
@@ -3677,14 +3677,6 @@ bool pci_acs_path_enabled(struct pci_dev *start,
void pci_acs_init(struct pci_dev *dev)
{
dev->acs_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
-
- /*
- * Attempt to enable ACS regardless of capability because some Root
- * Ports (e.g. those quirked with *_intel_pch_acs_*) do not have
- * the standard ACS capability but still support ACS via those
- * quirks.
- */
- pci_enable_acs(dev);
}

void pci_rebar_init(struct pci_dev *pdev)
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 565acfcd7cdb1..36cf1ffb2023c 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -920,6 +920,7 @@ static inline resource_size_t pci_resource_alignment(struct pci_dev *dev,
}

void pci_acs_init(struct pci_dev *dev);
+void pci_enable_acs(struct pci_dev *dev);
#ifdef CONFIG_PCI_QUIRKS
int pci_dev_specific_acs_enabled(struct pci_dev *dev, u16 acs_flags);
int pci_dev_specific_enable_acs(struct pci_dev *dev);
--
2.51.0