Re: [PATCH v7 4/5] iommu/of: Require reg for iommu-addresses

[Krzysztof Kozlowski <krzk@kernel.org>]

On 06/11/2026 18:14, Vikash Garodia wrote:
> The "iommu-addresses" property describes an identity 1:1 mapping between
> an IOVA range and the physical memory specified by "reg" in the same
> reserved-memory node. Without "reg", there is no physical memory to map.

This looks like ABI break.

> 
> The DT schema now requires "reg" whenever "iommu-addresses" is present.
> Align the kernel implementation with this requirement.
> https://github.com/devicetree-org/dt-schema/pull/207
> 
> An identity mapping requires matching IOVA and "reg" ranges. Reject
> mismatched ranges and report an error.
> 
> Suggested-by: Rob Herring <robh@kernel.org>
> Co-developed-by: Vishnu Reddy <busanna.reddy@oss.qualcomm.com>
> Signed-off-by: Vishnu Reddy <busanna.reddy@oss.qualcomm.com>
> Signed-off-by: Vikash Garodia <vikash.garodia@oss.qualcomm.com>
> ---
>  drivers/iommu/of_iommu.c | 32 +++++++++++++++-----------------
>  1 file changed, 15 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index 6675fc900e6c2d55b34c61dc9effaeb48e24f18f..00b02c19f27e195fc36c4bc1d91253255147c9ab 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -174,19 +174,12 @@ iommu_resv_region_get_type(struct device *dev,
>  {
>  	phys_addr_t end = start + length - 1;
>  
> -	/*
> -	 * IOMMU regions without an associated physical region cannot be
> -	 * mapped and are simply reservations.
> -	 */
> -	if (phys->start >= phys->end)
> -		return IOMMU_RESV_RESERVED;
> -
>  	/* may be IOMMU_RESV_DIRECT_RELAXABLE for certain cases */
>  	if (start == phys->start && end == phys->end)
>  		return IOMMU_RESV_DIRECT;
>  
> -	dev_warn(dev, "treating non-direct mapping [%pr] -> [%pap-%pap] as reservation\n", phys,
> -		 &start, &end);
> +	dev_err(dev, "non-direct mapping [%pr] -> [%pap-%pap] is not supported\n", phys,
> +		&start, &end);
>  	return IOMMU_RESV_RESERVED;
>  }
>  
> @@ -211,12 +204,14 @@ void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
>  		struct resource phys;
>  		int size;
>  
> -		memset(&phys, 0, sizeof(phys));
> +		maps = of_get_property(it.node, "iommu-addresses", &size);
> +		if (!maps)
> +			continue;
>  
>  		/*
> -		 * The "reg" property is optional and can be omitted by reserved-memory regions
> -		 * that represent reservations in the IOVA space, which are regions that should
> -		 * not be mapped.
> +		 * "iommu-addresses" must be used in combination with a "reg" that provides
> +		 * the physical address and size of this memory region, for an identity 1:1
> +		 * IOVA mapping to that physical memory.
>  		 */
>  		if (of_property_present(it.node, "reg")) {
>  			err = of_address_to_resource(it.node, 0, &phys);
> @@ -225,11 +220,11 @@ void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
>  					it.node, err);
>  				continue;
>  			}
> -		}
> -
> -		maps = of_get_property(it.node, "iommu-addresses", &size);
> -		if (!maps)

I miss the point why you are moving this part. Irrespective to actual
ABI break, why do you nee to check for iommu-addresses before?


Best regards,
Krzysztof