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

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Message-ID: <85a97019-2f80-4104-b27a-6578612af1e4@mailbox.org>
Date: Wed, 24 Sep 2025 05:34:55 +0200
From: Marek Vasut <marek.vasut@...lbox.org>
To: Manivannan Sadhasivam <mani@...nel.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

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 ...

> 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.