[PATCH] PCI: rcar-host: Add static assertion to check !PCI_LOCKLESS_CONFIG

[PATCH] PCI: rcar-host: Add static assertion to check !PCI_LOCKLESS_CONFIG

[Marek Vasut]

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@mailbox.org>
---
Cc: "Krzysztof Wilczyński" <kwilczynski@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: Manivannan Sadhasivam <mani@kernel.org>
Cc: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-pci@vger.kernel.org
Cc: linux-renesas-soc@vger.kernel.org
---
 drivers/pci/controller/pcie-rcar-host.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/pci/controller/pcie-rcar-host.c b/drivers/pci/controller/pcie-rcar-host.c
index 213028052aa58..29e13f7ff7ff1 100644
--- 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;
-- 
2.51.0

Re: [PATCH] PCI: rcar-host: Add static assertion to check !PCI_LOCKLESS_CONFIG

[Geert Uytterhoeven]

Hi Marek,

On Mon, 22 Sept 2025 at 17:34, Marek Vasut
<marek.vasut+renesas@mailbox.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@mailbox.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...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] PCI: rcar-host: Add static assertion to check !PCI_LOCKLESS_CONFIG

[Marek Vasut]

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@mailbox.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@mailbox.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.

Re: [PATCH] PCI: rcar-host: Add static assertion to check !PCI_LOCKLESS_CONFIG

[Marek Vasut]

On 9/22/25 5:48 PM, Marek Vasut wrote:

Hello Geert,

>>> +/*
>>> + * 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.

Maybe we can try with both.

-- 
Best regards,
Marek Vasut

Re: [PATCH] PCI: rcar-host: Add static assertion to check !PCI_LOCKLESS_CONFIG

[kernel test robot]

Hi Marek,

kernel test robot noticed the following build errors:

[auto build test ERROR on pci/next]
[also build test ERROR on pci/for-linus linus/master v6.17-rc7 next-20250922]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Marek-Vasut/PCI-rcar-host-Add-static-assertion-to-check-PCI_LOCKLESS_CONFIG/20250922-233709
base:   https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git next
patch link:    https://lore.kernel.org/r/20250922153352.99197-1-marek.vasut%2Brenesas%40mailbox.org
patch subject: [PATCH] PCI: rcar-host: Add static assertion to check !PCI_LOCKLESS_CONFIG
config: i386-allmodconfig (https://download.01.org/0day-ci/archive/20250923/202509231859.HdRgUtEm-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250923/202509231859.HdRgUtEm-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509231859.HdRgUtEm-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from include/linux/bits.h:30,
                    from include/linux/bitops.h:6,
                    from drivers/pci/controller/pcie-rcar-host.c:14:
>> include/linux/build_bug.h:78:41: error: static assertion failed: "!IS_ENABLED(CONFIG_PCI_LOCKLESS_CONFIG)"
      78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
         |                                         ^~~~~~~~~~~~~~
   include/linux/build_bug.h:77:34: note: in expansion of macro '__static_assert'
      77 | #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
         |                                  ^~~~~~~~~~~~~~~
   drivers/pci/controller/pcie-rcar-host.c:43:1: note: in expansion of macro 'static_assert'
      43 | static_assert(!IS_ENABLED(CONFIG_PCI_LOCKLESS_CONFIG));
         | ^~~~~~~~~~~~~


vim +78 include/linux/build_bug.h

bc6245e5efd70c Ian Abbott       2017-07-10  60  
6bab69c65013be Rasmus Villemoes 2019-03-07  61  /**
6bab69c65013be Rasmus Villemoes 2019-03-07  62   * static_assert - check integer constant expression at build time
6bab69c65013be Rasmus Villemoes 2019-03-07  63   *
6bab69c65013be Rasmus Villemoes 2019-03-07  64   * static_assert() is a wrapper for the C11 _Static_assert, with a
6bab69c65013be Rasmus Villemoes 2019-03-07  65   * little macro magic to make the message optional (defaulting to the
6bab69c65013be Rasmus Villemoes 2019-03-07  66   * stringification of the tested expression).
6bab69c65013be Rasmus Villemoes 2019-03-07  67   *
6bab69c65013be Rasmus Villemoes 2019-03-07  68   * Contrary to BUILD_BUG_ON(), static_assert() can be used at global
6bab69c65013be Rasmus Villemoes 2019-03-07  69   * scope, but requires the expression to be an integer constant
6bab69c65013be Rasmus Villemoes 2019-03-07  70   * expression (i.e., it is not enough that __builtin_constant_p() is
6bab69c65013be Rasmus Villemoes 2019-03-07  71   * true for expr).
6bab69c65013be Rasmus Villemoes 2019-03-07  72   *
6bab69c65013be Rasmus Villemoes 2019-03-07  73   * Also note that BUILD_BUG_ON() fails the build if the condition is
6bab69c65013be Rasmus Villemoes 2019-03-07  74   * true, while static_assert() fails the build if the expression is
6bab69c65013be Rasmus Villemoes 2019-03-07  75   * false.
6bab69c65013be Rasmus Villemoes 2019-03-07  76   */
6bab69c65013be Rasmus Villemoes 2019-03-07  77  #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
6bab69c65013be Rasmus Villemoes 2019-03-07 @78  #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
6bab69c65013be Rasmus Villemoes 2019-03-07  79  
07a368b3f55a79 Maxim Levitsky   2022-10-25  80  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki