On Wed, May 07, 2025 at 09:12:59AM +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

are removed

OR

consumer

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, a first approach
would be to use a finer grain and disable this support only for the
possible problematic subset of x86 systems (at least OLPC and CE4100).

This first approach could still leads to issues. Indeed, the list of
possible problematic system and the way to identify them using Kconfig
symbols is not well defined and so some system can be missed leading to
kernel regressions on those missing systems.

Use an other way and enable the support on x86 system only when this
support is needed by some specific feature. The usage of a device-tree
overlay by a PCI driver and thus the creation of PCI device-tree nodes
is a feature that needs it.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
link: https://lore.kernel.org/lkml/3c1f2473-92ad-bfc4-258e-a5a08ad73dd0@web.de/ (local) [0]

Link:

(mind capitalisation)

Otherwise LGTM, FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko