Re: [PATCH v4 19/29] of: property: Allow fw_devlink device-tree on x86

[Rob Herring]

On Wed, Oct 15, 2025 at 09:14:06AM +0200, Herve Codina wrote:
> PCI drivers can use a device-tree overlay to describe the hardware
> available on the PCI board. This is the case, for instance, of the
> LAN966x PCI device driver.
> 
> Adding some more nodes in the device-tree overlay adds some more
> consumer/supplier relationship between devices instantiated from this
> overlay.
> 
> Those fw_node consumer/supplier relationships are handled by fw_devlink
> and are created based on the device-tree parsing done by the
> of_fwnode_add_links() function.
> 
> Those consumer/supplier links are needed in order to ensure a correct PM
> runtime management and a correct removal order between devices.
> 
> For instance, without those links a supplier can be removed before its
> consumers is removed leading to all kind of issue if this consumer still
> want the use the already removed supplier.
> 
> The support for the usage of an overlay from a PCI driver has been added
> on x86 systems in commit 1f340724419ed ("PCI: of: Create device tree PCI
> host bridge node").
> 
> In the past, support for fw_devlink on x86 had been tried but this
> support has been removed in commit 4a48b66b3f52 ("of: property: Disable
> fw_devlink DT support for X86"). Indeed, this support was breaking some
> x86 systems such as OLPC system and the regression was reported in [0].
> 
> Instead of disabling this support for all x86 system, use a finer grain
> and disable this support only for the possible problematic subset of x86
> systems (at least OLPC and CE4100).
> 
> Those systems use a device-tree to describe their hardware. Identify
> those systems using key properties in the device-tree.
> 
> Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>
> Link: https://lore.kernel.org/lkml/3c1f2473-92ad-bfc4-258e-a5a08ad73dd0@xxxxxx/ [0]
> ---
>  drivers/of/property.c | 31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index c1feb631e383..09b568e3b826 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1600,12 +1600,41 @@ static int of_fwnode_irq_get(const struct fwnode_handle *fwnode,
>  	return of_irq_get(to_of_node(fwnode), index);
>  }
>  
> +static int match_property_by_path(const char *node_path, const char *prop_name,
> +				  const char *value)
> +{
> +	struct device_node *np __free(device_node) = of_find_node_by_path(node_path);
> +
> +	return of_property_match_string(np, prop_name, value);
> +}
> +
> +static bool of_is_fwnode_add_links_supported(void)
> +{
> +	static int is_supported = -1;
> +
> +	if (is_supported != -1)
> +		return !!is_supported;
> +

All of this:

> +	if (match_property_by_path("/soc", "compatible", "intel,ce4100-cp") >= 0)
> +		goto not_supported;
> +
> +	if (match_property_by_path("/", "architecture", "OLPC") >= 0)
> +		goto not_supported;
> +
> +	is_supported = 1;
> +	return !!is_supported;
> +
> +not_supported:
> +	is_supported = 0;

can be simplified to:

is_supported = !((match_property_by_path("/soc", "compatible", "intel,ce4100-cp") >= 0) || 
                 (match_property_by_path("/", "architecture", "OLPC") >= 0));

> +	return !!is_supported;
> +}
> +
>  static int of_fwnode_add_links(struct fwnode_handle *fwnode)
>  {
>  	const struct property *p;
>  	struct device_node *con_np = to_of_node(fwnode);
>  
> -	if (IS_ENABLED(CONFIG_X86))
> +	if (IS_ENABLED(CONFIG_X86) && !of_is_fwnode_add_links_supported())

I would move the IS_ENABLED() check to 
of_is_fwnode_add_links_supported().

Rob