Re: [PATCH v9 2/3] of: factor arguments passed to of_map_id() into a struct

[Marc Zyngier <maz@xxxxxxxxxx>]

On Sun, 01 Mar 2026 08:34:20 +0000,
Vijayanand Jitta <vijayanand.jitta@xxxxxxxxxxxxxxxx> wrote:
> 
> From: Charan Teja Kalla <charan.kalla@xxxxxxxxxxxxxxxx>
> 
> Change of_map_id() to take a pointer to struct of_phandle_args
> instead of passing target device node and translated IDs separately.
> Update all callers accordingly.
> 
> Subsequent patch will make use of the args_count field in
> struct of_phandle_args.
> 
> Suggested-by: Rob Herring (Arm) <robh@xxxxxxxxxx>
> Signed-off-by: Charan Teja Kalla <charan.kalla@xxxxxxxxxxxxxxxx>
> Signed-off-by: Vijayanand Jitta <vijayanand.jitta@xxxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/of_iommu.c              |  2 +-
>  drivers/of/base.c                     | 37 
> +++++++++++++++++------------------
>  drivers/pci/controller/dwc/pci-imx6.c |  8 +++++++-
>  drivers/pci/controller/pcie-apple.c   |  4 +++-
>  drivers/xen/grant-dma-ops.c           |  2 +-
>  include/linux/of.h                    | 21 +++++++++++++-------
>  6 files changed, 44 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index a511ecf21fcd..d255d0f58e8c 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -48,7 +48,7 @@ static int of_iommu_configure_dev_id(struct device_node 
> *master_np,
>       struct of_phandle_args iommu_spec = { .args_count = 1 };
>       int err;
>  
> -     err = of_map_iommu_id(master_np, *id, &iommu_spec.np, iommu_spec.args);
> +     err = of_map_iommu_id(master_np, *id, &iommu_spec);
>       if (err)
>               return err;
>  
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 57420806c1a2..6c3628255908 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -2102,8 +2102,11 @@ int of_find_last_cache_level(unsigned int cpu)
>   * @id: device ID to map.
>   * @map_name: property name of the map to use.
>   * @map_mask_name: optional property name of the mask to use.
> - * @target: optional pointer to a target device node.
> - * @id_out: optional pointer to receive the translated ID.
> + * @arg: of_phandle_args structure,
> + *   which includes:
> + *   np: pointer to the target device node
> + *   args_count: number of arguments

Number of arguments *to what*? Isn't that the size of args[] instead?

> + *   args[]: array to receive the translated ID(s).
>   *
>   * Given a device ID, look up the appropriate implementation-defined
>   * platform ID and/or the target device which receives transactions on that
> @@ -2117,21 +2120,21 @@ int of_find_last_cache_level(unsigned int cpu)
>   */
>  int of_map_id(const struct device_node *np, u32 id,
>              const char *map_name, const char *map_mask_name,
> -            struct device_node **target, u32 *id_out)
> +            struct of_phandle_args *arg)
>  {
>       u32 map_mask, masked_id;
>       int map_len;
>       const __be32 *map = NULL;
>  
> -     if (!np || !map_name || (!target && !id_out))
> +     if (!np || !map_name || !arg)
>               return -EINVAL;
>  
>       map = of_get_property(np, map_name, &map_len);
>       if (!map) {
> -             if (target)
> +             if (arg->np)
>                       return -ENODEV;
>               /* Otherwise, no map implies no translation */
> -             *id_out = id;
> +             arg->args[0] = id;

What if args_count is 0? Given that you place no restriction on the
way this can be called, that'd be entirely legitimate, and you'd
corrupt something you're not supposed to touch.

>               return 0;
>       }
>  
> @@ -2173,18 +2176,15 @@ int of_map_id(const struct device_node *np, u32 id,
>               if (!phandle_node)
>                       return -ENODEV;
>  
> -             if (target) {
> -                     if (*target)
> -                             of_node_put(phandle_node);
> -                     else
> -                             *target = phandle_node;
> +             if (arg->np)
> +                     of_node_put(phandle_node);
> +             else
> +                     arg->np = phandle_node;
>  
> -                     if (*target != phandle_node)
> -                             continue;
> -             }
> +             if (arg->np != phandle_node)
> +                     continue;
>  
> -             if (id_out)
> -                     *id_out = masked_id - id_base + out_base;
> +             arg->args[0] = masked_id - id_base + out_base;
>  
>               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, out_base,
> @@ -2193,11 +2193,10 @@ int of_map_id(const struct device_node *np, u32 id,
>       }
>  
>       pr_info("%pOF: no %s translation for id 0x%x on %pOF\n", np, map_name,
> -             id, target && *target ? *target : NULL);
> +             id, arg->np ? arg->np : NULL);
>  
>       /* Bypasses translation */
> -     if (id_out)
> -             *id_out = id;
> +     arg->args[0] = id;
>       return 0;
>  }
>  EXPORT_SYMBOL_GPL(of_map_id);
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c 
> b/drivers/pci/controller/dwc/pci-imx6.c
> index bff8289f804a..74fc603b3f84 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -1139,12 +1139,18 @@ static int imx_pcie_add_lut_by_rid(struct imx_pcie 
> *imx_pcie, u32 rid)
>  {
>       struct device *dev = imx_pcie->pci->dev;
>       struct device_node *target;
> +     struct of_phandle_args iommu_spec = { .args_count = 1 };
>       u32 sid_i, sid_m;
>       int err_i, err_m;
>       u32 sid = 0;
>  
>       target = NULL;
> -     err_i = of_map_iommu_id(dev->of_node, rid, &target, &sid_i);
> +     err_i = of_map_iommu_id(dev->of_node, rid, &iommu_spec);
> +     if (!err_i) {
> +             target = iommu_spec.np;
> +             sid_i = iommu_spec.args[0];
> +     }
> +
>       if (target) {
>               of_node_put(target);
>       } else {
> diff --git a/drivers/pci/controller/pcie-apple.c 
> b/drivers/pci/controller/pcie-apple.c
> index a0937b7b3c4d..e1d4b37d200d 100644
> --- a/drivers/pci/controller/pcie-apple.c
> +++ b/drivers/pci/controller/pcie-apple.c
> @@ -755,6 +755,7 @@ static int apple_pcie_enable_device(struct 
> pci_host_bridge *bridge, struct pci_d
>  {
>       u32 sid, rid = pci_dev_id(pdev);
>       struct apple_pcie_port *port;
> +     struct of_phandle_args iommu_spec = { .args_count = 1 };
>       int idx, err;
>  
>       port = apple_pcie_get_port(pdev);
> @@ -764,10 +765,11 @@ 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, NULL, &sid);
> +     err = of_map_iommu_id(port->pcie->dev->of_node, rid, &iommu_spec);
>       if (err)
>               return err;
>  
> +     sid = iommu_spec.args[0];

I find this stuff absolutely unreadable. You're fishing the SID in a
random position of a random structure, without any documentation of
how this is supposed to work. This really needs a wrapper that hides
this implementation detail.

Thanks,

        M.

-- 
Without deviation from the norm, progress is not possible.