Re: [PATCH v12 3/3] of: Respect #{iommu,msi}-cells in maps

[Vijayanand Jitta <vijayanand.jitta@xxxxxxxxxxxxxxxx>]

On 3/31/2026 7:34 PM, Vijayanand Jitta wrote:
> From: Robin Murphy <robin.murphy@xxxxxxx>
> 
> So far our parsing of {iommu,msi}-map properties has always blindly
> assumed that the output specifiers will always have exactly 1 cell.
> This typically does happen to be the case, but is not actually enforced
> (and the PCI msi-map binding even explicitly states support for 0 or 1
> cells) - as a result we've now ended up with dodgy DTs out in the field
> which depend on this behaviour to map a 1-cell specifier for a 2-cell
> provider, despite that being bogus per the bindings themselves.
> 
> Since there is some potential use in being able to map at least single
> input IDs to multi-cell output specifiers (and properly support 0-cell
> outputs as well), add support for properly parsing and using the target
> nodes' #cells values, albeit with the unfortunate complication of still
> having to work around expectations of the old behaviour too.
> 
> Since there are multi-cell output specifiers, the callers of of_map_id()
> may need to get the exact cell output value for further processing.
> Update of_map_id() to set args_count in the output to reflect the actual
> number of output specifier cells.
> 
> Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> Signed-off-by: Charan Teja Kalla <charan.kalla@xxxxxxxxxxxxxxxx>
> Signed-off-by: Vijayanand Jitta <vijayanand.jitta@xxxxxxxxxxxxxxxx>
> ---
>  drivers/of/base.c  | 155 
> ++++++++++++++++++++++++++++++++++++++++-------------
>  include/linux/of.h |   6 ++-
>  2 files changed, 123 insertions(+), 38 deletions(-)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index b3d002015192..7b22e2484e1c 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -2096,18 +2096,48 @@ int of_find_last_cache_level(unsigned int cpu)
>       return cache_level;
>  }
>  
> +/*
> + * Some DTs have an iommu-map targeting a 2-cell IOMMU node while
> + * specifying only 1 cell. Fortunately they all consist of value '1'
> + * as the 2nd cell entry with the same target, so check for that pattern.
> + *
> + * Example:
> + *   IOMMU node:
> + *           #iommu-cells = <2>;
> + *
> + *   Device node:
> + *           iommu-map = <0x0000 &smmu 0x0000 0x1>,
> + *                       <0x0100 &smmu 0x0100 0x1>;
> + */
> +static bool of_check_bad_map(const __be32 *map, int len)
> +{
> +     __be32 phandle = map[1];
> +
> +     if (len % 4)
> +             return false;
> +     for (int i = 0; i < len; i += 4) {
> +             if (map[i + 1] != phandle || map[i + 3] != cpu_to_be32(1))
> +                     return false;
> +     }
> +     return true;
> +}
> +
>  /**
>   * 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.
>   * @filter_np: optional device node to filter matches by, or NULL to match 
> any.
>   *   If non-NULL, only map entries targeting this node will be matched.
>   * @arg: pointer to a &struct of_phandle_args for the result. On success,
> - *   @arg->args[0] will contain the translated ID. If a map entry was
> - *   matched, @arg->np will be set to the target node with a reference
> - *   held that the caller must release with of_node_put().
> + *   @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. If a map entry was matched, @arg->np will be set
> + *   to the target node with a reference held that the caller must release
> + *   with of_node_put().
>   *
>   * Given a device ID, look up the appropriate implementation-defined
>   * platform ID and/or the target device which receives transactions on that
> @@ -2116,17 +2146,19 @@ int of_find_last_cache_level(unsigned int cpu)
>   * 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 *map_mask_name,
> +            const char *map_name, const char *cells_name,
> +            const char *map_mask_name,
>              const struct device_node *filter_np, struct of_phandle_args *arg)
>  {
>       u32 map_mask, masked_id;
> -     int map_len;
> +     int map_bytes, map_len, offset = 0;
> +     bool bad_map = false;
>       const __be32 *map = NULL;
>  
>       if (!np || !map_name || !arg)
>               return -EINVAL;
>  
> -     map = of_get_property(np, map_name, &map_len);
> +     map = of_get_property(np, map_name, &map_bytes);
>       if (!map) {
>               if (filter_np)
>                       return -ENODEV;
> @@ -2136,11 +2168,9 @@ int of_map_id(const struct device_node *np, u32 id,
>               return 0;
>       }
>  
> -     if (!map_len || map_len % (4 * sizeof(*map))) {
> -             pr_err("%pOF: Error: Bad %s length: %d\n", np,
> -                     map_name, map_len);
> -             return -EINVAL;
> -     }
> +     if (map_bytes % sizeof(*map))
> +             goto err_map_len;
> +     map_len = map_bytes / sizeof(*map);
>  
>       /* The default is to select all bits. */
>       map_mask = 0xffffffff;
> @@ -2153,39 +2183,82 @@ int of_map_id(const struct device_node *np, u32 id,
>               of_property_read_u32(np, map_mask_name, &map_mask);
>  
>       masked_id = map_mask & id;
> -     for ( ; map_len > 0; map_len -= 4 * sizeof(*map), map += 4) {
> +
> +     while (offset < map_len) {
>               struct device_node *phandle_node;
> -             u32 id_base = be32_to_cpup(map + 0);
> -             u32 phandle = be32_to_cpup(map + 1);
> -             u32 out_base = be32_to_cpup(map + 2);
> -             u32 id_len = be32_to_cpup(map + 3);
> +             u32 id_base, phandle, id_len, id_off, cells = 0;
> +             const __be32 *out_base;
> +
> +             if (map_len - offset < 2)
> +                     goto err_map_len;
> +
> +             id_base = be32_to_cpup(map + offset);
>  
>               if (id_base & ~map_mask) {
> -                     pr_err("%pOF: Invalid %s translation - %s-mask (0x%x) 
> ignores id-base (0x%x)\n",
> -                             np, map_name, map_name,
> -                             map_mask, id_base);
> +                     pr_err("%pOF: Invalid %s translation - %s (0x%x) 
> ignores id-base (0x%x)\n",
> +                            np, map_name, map_mask_name, map_mask, id_base);
>                       return -EFAULT;
>               }
>  
> -             if (masked_id < id_base || masked_id >= id_base + id_len)
> -                     continue;
> -
> +             phandle = be32_to_cpup(map + offset + 1);
>               phandle_node = of_find_node_by_phandle(phandle);
>               if (!phandle_node)
>                       return -ENODEV;
>  
> +             if (!bad_map && of_property_read_u32(phandle_node, cells_name, 
> &cells)) {
> +                     pr_err("%pOF: missing %s property\n", phandle_node, 
> cells_name);
> +                     of_node_put(phandle_node);
> +                     return -EINVAL;
> +             }
> +
> +             if (map_len - offset < 3 + cells) {
> +                     of_node_put(phandle_node);
> +                     goto err_map_len;
> +             }
> +
> +             if (offset == 0 && cells == 2) {
> +                     bad_map = of_check_bad_map(map, map_len);
> +                     if (bad_map) {
> +                             pr_warn_once("%pOF: %s mismatches target %s, 
> assuming extra cell of 0\n",
> +                                          np, map_name, cells_name);
> +                             cells = 1;
> +                     }
> +             }
> +
> +             out_base = map + offset + 2;
> +             offset += 3 + cells;
> +
> +             id_len = be32_to_cpup(map + offset - 1);
> +             if (id_len > 1 && cells > 1) {
> +                     /*
> +                      * With 1 output cell we reasonably assume its value
> +                      * has a linear relationship to the input; with more,
> +                      * we'd need help from the provider to know what to do.
> +                      */
> +                     pr_err("%pOF: Unsupported %s - cannot handle %d-ID 
> range with %d-cell output specifier\n",
> +                            np, map_name, id_len, cells);
> +                     of_node_put(phandle_node);
> +                     return -EINVAL;
> +             }
> +             id_off = masked_id - id_base;
> +             if (masked_id < id_base || id_off >= id_len) {
> +                     of_node_put(phandle_node);
> +                     continue;
> +             }
> +
>               if (filter_np && filter_np != phandle_node) {
>                       of_node_put(phandle_node);
>                       continue;
>               }
>  
>               arg->np = phandle_node;
> -             arg->args[0] = masked_id - id_base + out_base;
> -             arg->args_count = 1;
> +             for (int i = 0; i < cells; i++)
> +                     arg->args[i] = id_off + be32_to_cpu(out_base[i]);
> +             arg->args_count = cells;
>  
>               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,
> -                     id_len, id, masked_id - id_base + out_base);
> +                     np, map_name, map_mask, id_base, be32_to_cpup(out_base),
> +                     id_len, id, id_off + be32_to_cpup(out_base));
>               return 0;
>       }
>  
> @@ -2196,6 +2269,10 @@ int of_map_id(const struct device_node *np, u32 id,
>       arg->args[0] = id;
>       arg->args_count = 1;
>       return 0;
> +
> +err_map_len:
> +     pr_err("%pOF: Error: Bad %s length: %d\n", np, map_name, map_bytes);
> +     return -EINVAL;
>  }
>  EXPORT_SYMBOL_GPL(of_map_id);
>  
> @@ -2205,18 +2282,21 @@ EXPORT_SYMBOL_GPL(of_map_id);
>   * @id: Requester ID of the device (e.g. PCI RID/BDF or a platform
>   *      stream/device ID) used as the lookup key in the iommu-map table.
>   * @arg: pointer to a &struct of_phandle_args for the result. On success,
> - *   @arg->args[0] contains the translated ID. If a map entry was matched,
> - *   @arg->np holds a reference to the target node that the caller must
> - *   release with of_node_put().
> + *   @arg->args_count will be set to the number of output specifier cells
> + *   and @arg->args[0..args_count-1] will contain the translated output
> + *   specifier values. If a map entry was matched, @arg->np holds a
> + *   reference to the target node that the caller must release with
> + *   of_node_put().
>   *
> - * Convenience wrapper around of_map_id() using "iommu-map" and 
> "iommu-map-mask".
> + * Convenience wrapper around of_map_id() using "iommu-map", "#iommu-cells",
> + * and "iommu-map-mask".
>   *
>   * 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)
>  {
> -     return of_map_id(np, id, "iommu-map", "iommu-map-mask", NULL, arg);
> +     return of_map_id(np, id, "iommu-map", "#iommu-cells", "iommu-map-mask", 
> NULL, arg);
>  }
>  EXPORT_SYMBOL_GPL(of_map_iommu_id);
>  
> @@ -2229,17 +2309,20 @@ EXPORT_SYMBOL_GPL(of_map_iommu_id);
>   *   to match any. If non-NULL, only map entries targeting this node will
>   *   be matched.
>   * @arg: pointer to a &struct of_phandle_args for the result. On success,
> - *   @arg->args[0] contains the translated ID. If a map entry was matched,
> - *   @arg->np holds a reference to the target node that the caller must
> - *   release with of_node_put().
> + *   @arg->args_count will be set to the number of output specifier cells
> + *   and @arg->args[0..args_count-1] will contain the translated output
> + *   specifier values. If a map entry was matched, @arg->np holds a
> + *   reference to the target node that the caller must release with
> + *   of_node_put().
>   *
> - * Convenience wrapper around of_map_id() using "msi-map" and "msi-map-mask".
> + * Convenience wrapper around of_map_id() using "msi-map", "#msi-cells",
> + * and "msi-map-mask".
>   *
>   * Return: 0 on success or a standard error code on failure.
>   */
>  int of_map_msi_id(const struct device_node *np, u32 id,
>                 const struct device_node *filter_np, struct of_phandle_args 
> *arg)
>  {
> -     return of_map_id(np, id, "msi-map", "msi-map-mask", filter_np, arg);
> +     return of_map_id(np, id, "msi-map", "#msi-cells", "msi-map-mask", 
> filter_np, arg);
>  }
>  EXPORT_SYMBOL_GPL(of_map_msi_id);
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 8548cd9eb4f1..51ac8539f2c3 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -462,7 +462,8 @@ const char *of_prop_next_string(const struct property 
> *prop, const char *cur);
>  bool of_console_check(const struct device_node *dn, char *name, int index);
>  
>  int of_map_id(const struct device_node *np, u32 id,
> -            const char *map_name, const char *map_mask_name,
> +            const char *map_name, const char *cells_name,
> +            const char *map_mask_name,
>              const struct device_node *filter_np, struct of_phandle_args 
> *arg);
>  
>  int of_map_iommu_id(const struct device_node *np, u32 id,
> @@ -934,7 +935,8 @@ static inline void of_property_clear_flag(struct property 
> *p, unsigned long flag
>  }
>  
>  static inline int of_map_id(const struct device_node *np, u32 id,
> -                          const char *map_name, const char *map_mask_name,
> +                          const char *map_name, const char *cells_name,
> +                          const char *map_mask_name,
>                            const struct device_node *filter_np,
>                            struct of_phandle_args *arg)
>  {
> 

Gentle ping.

Thanks,
Vijay