linux-kernel - Re: [PATCH v2] PCI: rcar-host: Add static assertion to check !PCI_LOCKLESS

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Message-ID: <mc5sglju5r7zubnnuzmnl6nf2t5xdz7x6rqbx26dnl5hzvnyhi@ydp767j7gqx5>
Date: Wed, 24 Sep 2025 09:30:48 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Marek Vasut <marek.vasut@...lbox.org>
Cc: linux-pci@...r.kernel.org, 
	Krzysztof Wilczyński <kwilczynski@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Magnus Damm <magnus.damm@...il.com>, Marek Vasut <marek.vasut+renesas@...il.com>, 
	Rob Herring <robh@...nel.org>, Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, 
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v2] PCI: rcar-host: Add static assertion to check
 !PCI_LOCKLESS_CONFIG

On Wed, Sep 24, 2025 at 05:34:55AM +0200, Marek Vasut wrote:
> Hello Manivannan,
> 
> On 9/24/25 5:25 AM, Manivannan Sadhasivam wrote:
> > On Wed, Sep 24, 2025 at 01:46:18AM +0200, Marek Vasut wrote:
> > > This driver can not function correctly without PCIe subsystem level
> > > config space access serialization. In case PCI_LOCKLESS_CONFIG is
> > > ever enabled on ARM, complain loudly so the driver can be updated
> > > accordingly.
> > > 
> > 
> > This limitation applies to almost all host controller drivers except those used
> > on Intel platforms like VMD and Hyper-V. So this would require adding the
> > Kconfig dependency for all those, not just for RCAR.
> 
> Correct.
> 
> > We could also add the dependency to the arch Kconfig, but there is still a
> > possibility that if the driver is used on a platform selecting
> > PCI_LOCKLESS_CONFIG, it would be broken silently. So adding the dependency to
> > the individual drivers that suffer from the limitation seems to be the right
> > thing to do.
> 
> Would you like me to send a few more patches which add !PCI_LOCKLESS_CONFIG
> into per-driver Kconfig entries, at least for drivers where I am sure they
> suffer from this currently hypothetical issue ...
> 

Sure.

> > Also, I'm not in favor of adding static_assert with Kconfig dependency in place.
> ... and drop the static assert ?
> 
> Then the drivers would at least be marked accordingly.

Yes. Better than what we have currently.

- Mani

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