Re: [PATCH v7 5/5] iommu/of: Add support for "iommu-ranges" on a device node

[Yijie Yang <yijie.yang@oss.qualcomm.com>]

On 11/7/2026 1:14 AM, 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.
> "iommu-ranges" was introduced to specify the device specific IOVA ranges
> when there is no backing "reg".
> 
> Suggested-by: Rob Herring <robh@kernel.org>
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> 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 | 107 +++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 107 insertions(+)
> 
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index 00b02c19f27e195fc36c4bc1d91253255147c9ab..e133d3b346feecac7e2bfaec44e4882060ee89ec 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -183,6 +183,111 @@ 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;
> +		resource_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);
> +			goto exit;
> +		}
> +
> +		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);
> +			goto exit;
> +		}
> +
> +		prev = &ranges;
> +		list_for_each_entry(pos, &ranges, node) {
> +			if (pos->start > iova)
> +				break;
> +			prev = &pos->node;
> +		}
> +
> +		new = kmalloc_obj(*new);
> +		if (!new)
> +			goto exit;
> +
> +		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);

Why keep looping here after allocation failure?

> +		}
> +
> +		if (pos->end >= PHYS_ADDR_MAX - 1)
> +			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,
> +					 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
> @@ -262,5 +367,7 @@ void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
>   			}
>   		}
>   	}
> +
> +	of_iommu_derive_resv_regions(dev, list);
>   }
>   EXPORT_SYMBOL(of_iommu_get_resv_regions);
> 

-- 
Best Regards,
Yijie