Re: [PATCH v2] of/iommu: support multiple iommu-map entries per input ID

[Robin Murphy <robin.murphy@arm.com>]

On 2026-03-15 5:07 pm, Vijayanand Jitta wrote:
> When multiple mappings are present for an input ID, linux matches
> just the first one. There is a usecase [1] where all the mappings
> are to be maintained in parallel for an iommu-map entry of a same
> input id.
> 
> Add a next_offset iterator parameter to of_map_iommu_id() and
> refactor of_map_id() internals into a static helper to carry it.
> Update of_iommu_configure_dev_id() to loop over all matching
> entries to support this case. All other callers pass NULL and
> are unaffected.
> 
> [1] https://lore.kernel.org/all/20250627-video_cb-v3-0-51e18c0ffbce@quicinc.com/

That series doesn't even reference "iommu-map" though?

Once again, NAK to this - the purpose of "iommu-map"/"msi-map" is to 
describe a translation from one hardware ID space to another, where a 
one-to-many mapping of IDs to a single target would never make sense. 
While it is in principle possible for a single device to map to multiple 
different *targets*, that is ambiguous as to what it means - is it 
giving the OS a choice to use whichever one it prefers, or implying they 
must all be configured identically at all times? - so depending on how 
you prefer to look at it, we either do not support that, or we have 
chosen the first option.

> Signed-off-by: Vijayanand Jitta <vijayanand.jitta@oss.qualcomm.com>
> ---
> On Qualcomm kaanapali, the VPU hardware has multiple internal blocks
> that generate different stream IDs for the same input ID. The device
> tree encodes them as separate iommu-map entries sharing the same input
> ID:

And all that means is that your invented notion of "input IDs" is 
clearly wrong. Please stop this abuse of common bindings and just come 
up with a proper way to describe your hardware appropriately for what it 
actually is and does.

Thanks,
Robin.

>    iommu-map = <0x100 &apps_smmu 0x1940 0x1>,
>                <0x100 &apps_smmu 0x1a20 0x1>, ...
> 
> This requires multiple iommu-map entries per device.
> of_iommu_configure_dev_id() currently stops at the first match,
> so only one stream ID gets registered with the IOMMU.
> 
> The v1 series [1] addressed this with a callback threaded through
> of_map_id().
> 
> This patch uses a next_offset iterator on of_map_iommu_id() instead,
> keeping of_map_id() unchanged, and updates of_iommu_configure_dev_id()
> to loop over all matching entries.
> 
> This patch also depends on iommu-cells series [4].
> 
> Changes since v1:
>        - Split patches 2/7 [2] and 3/7 [3] out into this standalone series.
>        - Dropped the callback (of_map_id_cb / of_map_id_arg) entirely.
>        - Replaced with a next_offset iterator on of_map_iommu_id()
>      	only; of_map_id() public API is unchanged.
>        - of_iommu_configure_dev_id() now loops explicitly; no
>          bus-type heuristic (dev_is_platform()) needed.
> 
> [1] https://lore.kernel.org/all/20260126-kaanapali-iris-v1-0-e2646246bfc1@oss.qualcomm.com/
> [2] https://lore.kernel.org/all/20260126-kaanapali-iris-v1-2-e2646246bfc1@oss.qualcomm.com/
> [3] https://lore.kernel.org/all/20260126-kaanapali-iris-v1-3-e2646246bfc1@oss.qualcomm.com/
> [4] https://lore.kernel.org/all/ce25b963-0e8e-4411-a406-7b466eadb1f9@oss.qualcomm.com/
> 
> Signed-off-by: Vijayanand Jitta <vijayanand.jitta@oss.qualcomm.com>
> ---
>   drivers/iommu/of_iommu.c              | 20 +++++++----
>   drivers/of/base.c                     | 65 ++++++++++++++++++++++++++++++-----
>   drivers/pci/controller/dwc/pci-imx6.c |  2 +-
>   drivers/pci/controller/pcie-apple.c   |  2 +-
>   drivers/xen/grant-dma-ops.c           |  2 +-
>   include/linux/of.h                    |  4 +--
>   6 files changed, 75 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index a18bb60f6f3d..947eedd9a88b 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -46,14 +46,22 @@ static int of_iommu_configure_dev_id(struct device_node *master_np,
>   				     const u32 *id)
>   {
>   	struct of_phandle_args iommu_spec = {};
> -	int err;
> +	int offset = 0, err;
> +	bool found = false;
>   
> -	err = of_map_iommu_id(master_np, *id, &iommu_spec);
> -	if (err)
> -		return err;
> +	while (!(err = of_map_iommu_id(master_np, *id, &iommu_spec, &offset))) {
> +		err = of_iommu_xlate(dev, &iommu_spec);
> +		of_node_put(iommu_spec.np);
> +		iommu_spec.np = NULL;
> +		if (err)
> +			return err;
> +		found = true;
> +	}
> +
> +	/* -ENODEV means all entries exhausted; success if at least one was processed */
> +	if (err == -ENODEV && found)
> +		return 0;
>   
> -	err = of_iommu_xlate(dev, &iommu_spec);
> -	of_node_put(iommu_spec.np);
>   	return err;
>   }
>   
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 9c44eb6d445d..71175e670757 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -2146,13 +2146,13 @@ static bool of_check_bad_map(const __be32 *map, int len)
>    *
>    * Return: 0 on success or a standard error code on failure.
>    */
> -int of_map_id(const struct device_node *np, u32 id,
> -	       const char *map_name, const char *cells_name,
> -	       const char *map_mask_name,
> -	       struct of_phandle_args *arg)
> +static int of_map_id_next(const struct device_node *np, u32 id,
> +			  const char *map_name, const char *cells_name,
> +			  const char *map_mask_name,
> +			  struct of_phandle_args *arg, int *next_offset)
>   {
>   	u32 map_mask, masked_id;
> -	int map_bytes, map_len, offset = 0;
> +	int map_bytes, map_len, offset = next_offset ? *next_offset : 0;
>   	bool bad_map = false;
>   	const __be32 *map = NULL;
>   
> @@ -2161,7 +2161,7 @@ int of_map_id(const struct device_node *np, u32 id,
>   
>   	map = of_get_property(np, map_name, &map_bytes);
>   	if (!map) {
> -		if (arg->np)
> +		if (arg->np || next_offset)
>   			return -ENODEV;
>   		/* Otherwise, no map implies no translation */
>   		arg->args[0] = id;
> @@ -2262,9 +2262,16 @@ int of_map_id(const struct device_node *np, u32 id,
>   		pr_debug("%pOF: %s, using mask %08x, id-base: %08x, out-base: %08x, length: %08x, id: %08x -> %08x\n",
>   			np, map_name, map_mask, id_base, be32_to_cpup(out_base),
>   			id_len, id, id_off + be32_to_cpup(out_base));
> +
> +		if (next_offset)
> +			*next_offset = offset;	/* caller resumes from here */
>   		return 0;
>   	}
>   
> +	/* no (more) matches found in the map */
> +	if (next_offset)
> +		return -ENODEV;
> +
>   	pr_info("%pOF: no %s translation for id 0x%x on %pOF\n", np, map_name,
>   		id, arg->np);
>   
> @@ -2276,6 +2283,38 @@ int of_map_id(const struct device_node *np, u32 id,
>   	pr_err("%pOF: Error: Bad %s length: %d\n", np, map_name, map_bytes);
>   	return -EINVAL;
>   }
> +
> +/**
> + * of_map_id - Translate an ID through a downstream mapping.
> + * @np: root complex device node.
> + * @id: device ID to map.
> + * @map_name: property name of the map to use.
> + * @cells_name: property name of target specifier cells.
> + * @map_mask_name: optional property name of the mask to use.
> + * @arg: pointer to a &struct of_phandle_args. On input, @arg->np may be
> + *	set to a target device node to match, or NULL to match any. On
> + *	success, @arg->np will be set to the matched target node (with a
> + *	reference held), @arg->args_count will be set to the number of
> + *	output specifier cells as defined by @cells_name in the target node,
> + *	and @arg->args[0..args_count-1] will contain the translated output
> + *	specifier values.
> + *
> + * Given a device ID, look up the appropriate implementation-defined
> + * platform ID and/or the target device which receives transactions on that
> + * ID, as per the "iommu-map" and "msi-map" bindings. If @arg->np points to
> + * a non-NULL device node, only entries targeting that node will be matched;
> + * if it is NULL, it will receive the device node of the first matching
> + * target phandle, with a reference held.
> + *
> + * Return: 0 on success or a standard error code on failure.
> + */
> +int of_map_id(const struct device_node *np, u32 id,
> +	      const char *map_name, const char *cells_name,
> +	      const char *map_mask_name,
> +	      struct of_phandle_args *arg)
> +{
> +	return of_map_id_next(np, id, map_name, cells_name, map_mask_name, arg, NULL);
> +}
>   EXPORT_SYMBOL_GPL(of_map_id);
>   
>   /**
> @@ -2285,15 +2324,23 @@ EXPORT_SYMBOL_GPL(of_map_id);
>    * @arg: pointer to a &struct of_phandle_args for the result. On success,
>    *	@arg->np holds a reference to the target node that the caller must
>    *	release with of_node_put().
> + * @next_offset: if non-NULL, on success it is set to the map offset just
> + *	past the matched entry. Pass this value back on the next call to
> + *	resume scanning from where the previous call left off, allowing all
> + *	matching entries for the same @id to be iterated. Pass NULL (or a
> + *	pointer to 0) to find only the first match.
>    *
> - * Convenience wrapper around of_map_id() using "iommu-map" and "iommu-map-mask".
> + * Wrapper around the internal iommu-map scanner using "iommu-map" and
> + * "iommu-map-mask". When @next_offset is non-NULL, returns -ENODEV once
> + * all matching entries have been exhausted.
>    *
>    * Return: 0 on success or a standard error code on failure.
>    */
>   int of_map_iommu_id(const struct device_node *np, u32 id,
> -		    struct of_phandle_args *arg)
> +		    struct of_phandle_args *arg, int *next_offset)
>   {
> -	return of_map_id(np, id, "iommu-map", "#iommu-cells", "iommu-map-mask", arg);
> +	return of_map_id_next(np, id, "iommu-map", "#iommu-cells",
> +			      "iommu-map-mask", arg, next_offset);
>   }
>   EXPORT_SYMBOL_GPL(of_map_iommu_id);
>   
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 5f8a11774eb5..0d7f5e6d037a 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -1146,7 +1146,7 @@ static int imx_pcie_add_lut_by_rid(struct imx_pcie *imx_pcie, u32 rid)
>   	u32 sid = 0;
>   
>   	target = NULL;
> -	err_i = of_map_iommu_id(dev->of_node, rid, &iommu_spec);
> +	err_i = of_map_iommu_id(dev->of_node, rid, &iommu_spec, NULL);
>   	if (!err_i) {
>   		target = iommu_spec.np;
>   		sid_i = iommu_spec.args[0];
> diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
> index 2e86f8fd300b..c780e3f9d14d 100644
> --- a/drivers/pci/controller/pcie-apple.c
> +++ b/drivers/pci/controller/pcie-apple.c
> @@ -765,7 +765,7 @@ static int apple_pcie_enable_device(struct pci_host_bridge *bridge, struct pci_d
>   	dev_dbg(&pdev->dev, "added to bus %s, index %d\n",
>   		pci_name(pdev->bus->self), port->idx);
>   
> -	err = of_map_iommu_id(port->pcie->dev->of_node, rid, &iommu_spec);
> +	err = of_map_iommu_id(port->pcie->dev->of_node, rid, &iommu_spec, NULL);
>   	if (err)
>   		return err;
>   
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index 36547d7cf1d6..062beb5825f5 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -325,7 +325,7 @@ static int xen_dt_grant_init_backend_domid(struct device *dev,
>   		struct pci_dev *pdev = to_pci_dev(dev);
>   		u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
>   
> -		if (of_map_iommu_id(np, rid, &iommu_spec)) {
> +		if (of_map_iommu_id(np, rid, &iommu_spec, NULL)) {
>   			dev_dbg(dev, "Cannot translate ID\n");
>   			return -ESRCH;
>   		}
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 953f2dbe0e86..990849f00e74 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -467,7 +467,7 @@ int of_map_id(const struct device_node *np, u32 id,
>   	       struct of_phandle_args *arg);
>   
>   int of_map_iommu_id(const struct device_node *np, u32 id,
> -		    struct of_phandle_args *arg);
> +		    struct of_phandle_args *arg, int *next_offset);
>   
>   int of_map_msi_id(const struct device_node *np, u32 id,
>   		  struct of_phandle_args *arg);
> @@ -943,7 +943,7 @@ static inline int of_map_id(const struct device_node *np, u32 id,
>   }
>   
>   static inline int of_map_iommu_id(const struct device_node *np, u32 id,
> -				  struct of_phandle_args *arg)
> +				  struct of_phandle_args *arg, int *next_offset)
>   {
>   	return -EINVAL;
>   }
> 
> ---
> base-commit: 9e94742cffb7541f55fa904a40c1ca9d836d303d
> change-id: 20260315-iommu_multi_map-8c9b78490ace
> 
> Best regards,