Re: [PATCH v2 1/2] PCI: Add PCI device flag PCI_DEV_FLAGS_DMA_ALIAS_ROOT

[Robin Murphy <robin.murphy@arm.com>]

On 08/05/16 10:33, Jayachandran C via iommu wrote:
> Add a new flag PCI_DEV_FLAGS_DMA_ALIAS_ROOT to limit the DMA alias
> search to go no further than the bridge where the IOMMU is attached.
>
> This has been added to support Broadcom's Vulcan which has the SMMUv3
> and GIC ITS associated with an intermediate bridge in the PCI topology.
> Traversing to buses above would hit internal glue bridges which will
> change the RID.

Can you not just have the relevant callback function detect the relevant 
node and terminate the walk of its own accord? That's what I was aiming 
for in this patch for the IOMMU setup:

http://article.gmane.org/gmane.linux.kernel.iommu/12456

Is there some flaw in that approach I've missed?

Robin.

> Update the function pci_for_each_dma_alias() to stop when it see a
> bridge with this flag set.
>
> Signed-off-by: Jayachandran C <jchandra@broadcom.com>
> ---
>
> Here is v2 of the patch, the previous discussion is at
> http://lists.linuxfoundation.org/pipermail/iommu/2016-February/015668.html
>
> v1->v2 changes:
>   - dropped the BAR quirk (not needed)
>   - moved from using the 'skip' flag for some bridges to using
>     similar approach to stop the traversal at the bridge with
>     PCI_DEV_FLAGS_DMA_ALIAS_ROOT
>
> Comments and suggestions are welcome
>
> JC.
>
>   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 a20ce7d..3ea9c27 100644
> --- a/drivers/pci/search.c
> +++ b/drivers/pci/search.c
> @@ -56,6 +56,10 @@ 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_DMA_ALIAS_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 932ec74..b6f832b 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -176,6 +176,8 @@ 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_DMA_ALIAS_ROOT = (__force pci_dev_flags_t) (1 << 9),
>   };
>
>   enum pci_irq_reroute_variant {
>