linux-kernel - Re: [PATCH v2 17/26] of: property: Allow fw_devlink device-tree on x86 when PCI device-tree node creation is enabled

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Message-ID: <aB0Dwdr8IJF4F9gR@smile.fi.intel.com>
Date: Thu, 8 May 2025 22:19:29 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Andrew Lunn <andrew@...n.ch>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
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	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 17/26] of: property: Allow fw_devlink device-tree on
 x86 when PCI device-tree node creation is enabled

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@...tlin.com>
> link: https://lore.kernel.org/lkml/3c1f2473-92ad-bfc4-258e-a5a08ad73dd0@web.de/ [0]

Link:

(mind capitalisation)

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

-- 
With Best Regards,
Andy Shevchenko