Re: [PATCH v6 2/2] of: Add support for "iommu-ranges" on a device node

[Rob Herring <robh@kernel.org>]

On Tue, Nov 03, 2026 at 08:59:33PM +0530, 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 | 134 +++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 125 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index 5c266511db78910d6fd221af5437cecff4931c22..0428ceb50dec58f11872b4fb64e283fa8d9046a3 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -185,11 +185,118 @@ iommu_resv_region_get_type(struct device *dev,
>  	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;
>  }
>  
> +/**
> + * 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.
> + */
> +#if IS_ENABLED(CONFIG_OF_ADDRESS)

Is this really needed? Assuming CONFIG_OF is enabled, this is only false 
on Sparc. I don't think Sparc needs anything in this file. There 
aren't any IOMMU drivers for Sparc unless COMPILE_TEST is enabled. So 
maybe building of_iommu.c as a whole should depend on CONFIG_OF_ADDRESS?

Rob