Re: [PATCH v5 04/13] iommu: of_iommu: Add support for "iommu-ranges" on a device node

[Bryan O'Donoghue <bryan.odonoghue@linaro.org>]

On 26/09/2026 07:34, Vikash Garodia wrote:
> Reserving an IOVA address using "iommu-addresses" requires it to be
> placed in the reserved-memory node. But when "iommu-addresses" is the
> only property being described and there is no backing "reg" (i.e. no
> actual reserved system memory), it does not really belong under
> /reserved-memory. A device IOVA range is specific to its own address
> space, and does not describe the system physical memory to make it
> qualify under reserved-memory. Given this, place "iommu-addresses"
> inside reserved-memory only when it is paired with a "reg", otherwise,
> define it within the device own node. It was discussed here:
> https://lore.kernel.org/all/662f7093-fb0a-4564-9ca0-98e03e68ba9a@kernel.org
> 
> Existing "iommu-addresses" property expects a phandle, which does
> not make sense when the property is defined within the device node.
> Introduce a new property, "iommu-ranges", to specify the device
> specific IOVA ranges when there is no backing "reg".
> 
> 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 | 128 ++++++++++++++++++++++++++++++++++++++++++++---
>   1 file changed, 121 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index a18bb60f6f3dfdba853b6e16dd2a8616f6a731c7..9766a6944d0e11a6cd8b74b1b89428acffe3dfdf 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -190,6 +190,111 @@ iommu_resv_region_get_type(struct device *dev,
>   	return IOMMU_RESV_RESERVED;
>   }
>   
> +/**
> + * of_iommu_derive_resv_regions - derive reserved regions which
> + *                                are outside of iommu-ranges
> + * @dev: device for which to get reserved regions
> + * @list: reserved region list
> + *
> + * A device can describe its own usable IOVA ranges directly on its node
> + * via "iommu-ranges". Everything not under those ranges is derived
> + * as a reserved region so the IOMMU allocator won't use it. Entries may
> + * appear in any order in the property.
> + */
> +static void of_iommu_derive_resv_regions(struct device *dev, struct list_head *list)
> +{
> +	struct of_iommu_range {
> +		struct list_head node;
> +		phys_addr_t start;
> +		phys_addr_t end;
> +	} *pos, *new, *next_range;
> +	int size, prot = IOMMU_READ | IOMMU_WRITE;
> +	struct iommu_resv_region *region;
> +	const __be32 *maps, *end;
> +	struct list_head *prev;
> +	phys_addr_t next = 0;
> +	LIST_HEAD(ranges);
> +
> +	maps = of_get_property(dev->of_node, "iommu-ranges", &size);
> +	if (!maps)
> +		return;
> +
> +	end = maps + size / sizeof(__be32);
> +
> +	while (maps < end) {
> +		phys_addr_t iova, iova_end;
> +		size_t length;
> +
> +		maps = of_translate_dma_region(dev->of_node, maps, &iova, &length);
> +		if (!maps) {
> +			dev_err(dev, "%pOF: failed to parse iommu-ranges\n",
> +				dev->of_node);
> +			break;
> +		}
> +
> +		if (!length)
> +			continue;
> +
> +		iova_end = iova + length - 1;
> +
> +		if (iova_end < iova) {
> +			dev_err(dev, "%pOF: iommu-ranges overflows address space\n",
> +				dev->of_node);
> +			continue;
> +		}
> +
> +		prev = &ranges;
> +		list_for_each_entry(pos, &ranges, node) {
> +			if (pos->start > iova)
> +				break;
> +			prev = &pos->node;
> +		}
> +
> +		new = kmalloc_obj(*new);
> +		if (!new)
> +			continue;
> +
> +		new->start = iova;
> +		new->end = iova_end;
> +		list_add(&new->node, prev);
> +	}
> +
> +	if (list_empty(&ranges))
> +		return;
> +
> +	if (of_dma_is_coherent(dev->of_node))
> +		prot |= IOMMU_CACHE;
> +
> +	list_for_each_entry_safe(pos, next_range, &ranges, node) {
> +		if (pos->start > next) {
> +			region = iommu_alloc_resv_region(next, pos->start - next, prot,
> +							 IOMMU_RESV_RESERVED, GFP_KERNEL);
> +			if (region)
> +				list_add_tail(&region->list, list);
> +		}
> +
> +		if (pos->end == PHYS_ADDR_MAX)
> +			goto exit;
> +
> +		if (pos->end >= next)
> +			next = pos->end + 1;
> +
> +		list_del(&pos->node);
> +		kfree(pos);
> +	}
> +
> +	region = iommu_alloc_resv_region(next, PHYS_ADDR_MAX - next + 1,
> +					 prot, IOMMU_RESV_RESERVED, GFP_KERNEL);
> +	if (region)
> +		list_add_tail(&region->list, list);
> +
> +exit:
> +	list_for_each_entry_safe(pos, next_range, &ranges, node) {
> +		list_del(&pos->node);
> +		kfree(pos);
> +	}
> +}
> +
>   /**
>    * of_iommu_get_resv_regions - reserved region driver helper for device tree
>    * @dev: device for which to get reserved regions
> @@ -214,10 +319,14 @@ void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
>   
>   		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);
> @@ -226,11 +335,11 @@ 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)
> +		} else {
> +			dev_err(dev, "%pOF: iommu-addresses requires a reg property\n",
> +				it.node);
>   			continue;
> +		}

The if/else doesn't belong in a path entitled 'Add support for 
"iommu-ranges"' as this changes he behaviour of iommu-addresses 
independently of whatever iommu-ranges does.

The reg update part basically has nothing to do with this series at all 
i.e. the code you depend on later in this series doesn't declare 
iommu-addresses so... this is an update to align with a DT schema change.

https://github.com/devicetree-org/dt-schema/pull/207

Perhaps splitting this into two patches as an iommu-series would be best.
>   
>   		end = maps + size / sizeof(__be32);
>   
> @@ -258,6 +367,9 @@ void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
>   				}
>   				type = iommu_resv_region_get_type(dev, &phys, iova, length);
>   
> +				if (type != IOMMU_RESV_DIRECT)
> +					continue;
> +

If you look in iommu_resv_region_get_type() you can emit

         dev_warn(dev, "treating non-direct mapping [%pr] -> [%pap-%pap] 
as reservation\n", phys,
                  &start, &end);
         return IOMMU_RESV_RESERVED;

on a mismatch - which is not what the code will do now. Mismatch will 
warn and then not map.

So maybe dev_err() saying you won't map - in the new patch for reg. 
Either way this isn't a change specific to iommu-ranges.

>   				region = iommu_alloc_resv_region(iova, length, prot, type,
>   								 GFP_KERNEL);
>   				if (region)
> @@ -265,6 +377,8 @@ void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
>   			}
>   		}
>   	}
> +
> +	of_iommu_derive_resv_regions(dev, list);
>   #endif
>   }
>   EXPORT_SYMBOL(of_iommu_get_resv_regions);
>