Re: [PATCH v6] i2c: mux: reg: use device property accessors

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

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On Tue, May 19, 2026 at 02:18:50PM -0700, Abdurrahman Hussain wrote:
> Convert the device-tree parsing path to the generic fwnode/device
> property accessors so the driver can be probed on ACPI and swnode
> platforms as well as OF. The helper is renamed from
> i2c_mux_reg_probe_dt() to i2c_mux_reg_probe_fw() to reflect that.
> 
> Accessor translation:
> 
>   of_parse_phandle("i2c-parent") +
>     of_find_i2c_adapter_by_node()    -> fwnode_find_reference() +
>                                          i2c_find_adapter_by_fwnode()
>   of_get_child_count()               -> device_get_child_node_count()
>   of_property_read_bool()            -> device_property_read_bool()
>   for_each_child_of_node()           -> device_for_each_child_node()
>     of_property_read_u32("reg")        on ACPI device nodes:
>                                          acpi_get_local_address()
>                                        everything else (OF, swnode,
>                                        ACPI data nodes):
>                                          fwnode_property_read_u32()
>   of_property_read_u32("idle-state") -> device_property_read_u32()
> 
> The child-node branch uses is_acpi_device_node() rather than
> is_acpi_node(): the latter also matches ACPI data nodes (the
> _DSD hierarchical-property children used by PRP0001-style
> firmware), which have no ACPI handle and would make
> acpi_get_local_address() fall back to evaluating _ADR against the
> root namespace and return -ENODATA.  Routing data nodes through
> fwnode_property_read_u32() instead lets them resolve the "reg"
> property the same way OF and swnode children do.
> 
> Behavioural preservations (deliberate, to avoid regressing existing
> users):
> 
>   - The three-way endian fallback is kept verbatim: an explicit
>     "little-endian" property wins, then "big-endian", and otherwise
>     the host's compile-time byte order. device_is_big_endian() is
>     not used here because it ignores "little-endian" and introduces
>     "native-endian" semantics, which would diverge from the binding.
> 
>   - The "if (!mux->data.reg)" guard around
>     devm_platform_get_and_ioremap_resource() in probe() is kept.
>     drivers/platform/mellanox/mlx-platform.c registers i2c-mux-reg
>     platform_devices with no memory resource and supplies a
>     pre-set .reg / .reg_size through struct
>     i2c_mux_reg_platform_data; without the guard those
>     registrations would fail in probe().
> 
>   - The "if (!mux->data.reg)" ioremap block (and the paired
>     reg_size validation that depends on it) is hoisted above
>     i2c_get_adapter(mux->data.parent), so the fwnode path
>     preserves master's ordering of "ioremap before parent-adapter
>     get".  For platdata users the validation runs from a slightly
>     earlier position, but mux->data.reg_size is already set from
>     platdata by then, so the order is functionally neutral.
> 
> The OF-only of_address_to_resource() translation in the old
> probe_dt() is dropped because the same address is available from
> the platform_device resource table on OF as well as ACPI, and the
> existing fallback in probe() ioremaps it.
> 
> Acked-by: Peter Rosin <peda@lysator.liu.se>
> Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
> Assisted-by: Claude-Code:claude-opus-4-7
> Assisted-by: sashiko:gemini-3.1-pro-preview

Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>


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