Re: [PATCH v3 3/7] PCI: OF: Allow endpoints to bypass the iommu

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s/iommu/IOMMU/ in subject

On Fri, Oct 12, 2018 at 03:59:13PM +0100, Jean-Philippe Brucker wrote:
> Using the iommu-map binding, endpoints in a given PCI domain can be
> managed by different IOMMUs. Some virtual machines may allow a subset of
> endpoints to bypass the IOMMU. In some case the IOMMU itself is presented

s/case/cases/

> as a PCI endpoint (e.g. AMD IOMMU and virtio-iommu). Currently, when a
> PCI root complex has an iommu-map property, the driver requires all
> endpoints to be described by the property. Allow the iommu-map property to
> have gaps.

I'm not an IOMMU or virtio expert, so it's not obvious to me why it is
safe to allow devices to bypass the IOMMU.  Does this mean a typo in
iommu-map could inadvertently allow devices to bypass it?  Should we
indicate something in dmesg (and/or sysfs) about devices that bypass
it?

> Relaxing of_pci_map_rid also allows the msi-map property to have gaps,

s/of_pci_map_rid/of_pci_map_rid()/

> which is invalid since MSIs always reach an MSI controller. Thankfully
> Linux will error out later, when attempting to find an MSI domain for the
> device.

Not clear to me what "error out" means here.  In a userspace program,
I would infer that the program exits with an error message, but I
doubt you mean that Linux exits.

> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
> ---
>  drivers/pci/of.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index 1836b8ddf292..2f5015bdb256 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -451,9 +451,10 @@ int of_pci_map_rid(struct device_node *np, u32 rid,
>  		return 0;
>  	}
>  
> -	pr_err("%pOF: Invalid %s translation - no match for rid 0x%x on %pOF\n",
> -		np, map_name, rid, target && *target ? *target : NULL);
> -	return -EFAULT;
> +	/* Bypasses translation */
> +	if (id_out)
> +		*id_out = rid;
> +	return 0;
>  }
>  
>  #if IS_ENABLED(CONFIG_OF_IRQ)
> -- 
> 2.19.1
> 
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