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PCI: Enable ACS after configuring IOMMU for OF platforms

Browse Source 
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
This commit is contained in:
Manivannan Sadhasivam 2026-01-02 21:04:47 +05:30 committed by Bjorn Helgaas
parent 5907a90551
commit c41e2fb67e
3 changed files with 10 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/pci/pci-driver.c
View File

@ -1650,6 +1650,14 @@ 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 */

10
drivers/pci/pci.c
View File

@ -1016,7 +1016,7 @@ 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;
@ -3649,14 +3649,6 @@ 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);
}
/**

1
drivers/pci/pci.h
View File

@ -939,6 +939,7 @@ 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);