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

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Message-ID: <974b6f7f-e769-48ff-9bd9-0ed0c8f48b1e@mailbox.org>
Date: Mon, 22 Sep 2025 17:48:40 +0200
From: Marek Vasut <marek.vasut@...lbox.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>,
 Marek Vasut <marek.vasut+renesas@...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>, Manivannan Sadhasivam
 <mani@...nel.org>, 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] PCI: rcar-host: Add static assertion to check
 !PCI_LOCKLESS_CONFIG

On 9/22/25 5:41 PM, Geert Uytterhoeven wrote:

Hello Geert,

> On Mon, 22 Sept 2025 at 17:34, Marek Vasut
> <marek.vasut+renesas@...lbox.org> 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.
>>
>> Signed-off-by: Marek Vasut <marek.vasut+renesas@...lbox.org>
> 
> Thanks for your patch!
> 
>> --- a/drivers/pci/controller/pcie-rcar-host.c
>> +++ b/drivers/pci/controller/pcie-rcar-host.c
>> @@ -35,6 +35,14 @@
>>
>>   #include "pcie-rcar.h"
>>
>> +/*
>> + * 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.
>> + */
>> +static_assert(!IS_ENABLED(CONFIG_PCI_LOCKLESS_CONFIG));
>> +
>>   struct rcar_msi {
>>          DECLARE_BITMAP(used, INT_PCI_MSI_NR);
>>          struct irq_domain *domain;
> 
> This causes a build failure when compile-testing, e.g. x86 allmodconfig.
> Using "depends on !PCI_LOCKLESS_CONFIG" instead would avoid that,
> but indeed has the disadvantage that it wouldn't complain loudly when
> PCI_LOCKLESS_CONFIG would ever be enabled on ARM64...
All right, let's also wait for input from PCI maintainers. It seems both 
alternatives -- static_assert() and !PCI_LOCKLESS_CONFIG have their own 
disadvantages, maybe there is a third option.