[PATCH v4 1/2] PCI: Add device flag PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT

[Robin Murphy]

On 03/04/17 14:15, Jayachandran C wrote:
> Add a new quirk flag PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT to limit the DMA
> alias search to go no further than the bridge where the IOMMU unit is
> attached.
> 
> The flag will be used to indicate a bridge device which forwards the
> address translation requests to the IOMMU, i.e where the interrupt and
> DMA requests leave the PCIe hierarchy and go into the system blocks.
> 
> Usually this happens at the PCI RC, so this flag is not needed. But
> on systems where there are bridges that introduce aliases above the
> "real" root bridge, this flag is needed to ensure that the function
> pci_for_each_dma_alias() works correctly.
> 
> The function pci_for_each_dma_alias() is updated to stop when it see a
> bridge with this flag set.

As it seems to have been me positing most of the alternative
suggestions, which have indeed turned out to have holes in (no, I can't
see how we'd cleanly fix pci_device_group() either), I'll stand by my
earlier "(I have no actual objection to this patch, though, [...])":

Reviewed-by: Robin Murphy <robin.murphy at arm.com>

> Signed-off-by: Jayachandran C <jnair at caviumnetworks.com>
> ---
>  drivers/pci/search.c | 4 ++++
>  include/linux/pci.h  | 2 ++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/search.c b/drivers/pci/search.c
> index 33e0f03..4c6044a 100644
> --- a/drivers/pci/search.c
> +++ b/drivers/pci/search.c
> @@ -60,6 +60,10 @@ int pci_for_each_dma_alias(struct pci_dev *pdev,
>  
>  		tmp = bus->self;
>  
> +		/* stop at bridge where translation unit is associated */
> +		if (tmp->dev_flags & PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT)
> +			return ret;
> +
>  		/*
>  		 * PCIe-to-PCI/X bridges alias transactions from downstream
>  		 * devices using the subordinate bus number (PCI Express to
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index eb3da1a..3f596ac 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -178,6 +178,8 @@ enum pci_dev_flags {
>  	PCI_DEV_FLAGS_NO_PM_RESET = (__force pci_dev_flags_t) (1 << 7),
>  	/* Get VPD from function 0 VPD */
>  	PCI_DEV_FLAGS_VPD_REF_F0 = (__force pci_dev_flags_t) (1 << 8),
> +	/* a non-root bridge where translation occurs, stop alias search here */
> +	PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT = (__force pci_dev_flags_t) (1 << 9),
>  };
>  
>  enum pci_irq_reroute_variant {
>