Re: [PATCH] i915: fix build error some more

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Fri, Jun 20, 2025 at 01:18:18PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> An earlier patch fixed a build failure with clang, but I still see the
> same problem with some configurations using gcc:
> 
> drivers/gpu/drm/i915/i915_pmu.c: In function 'config_mask':
> include/linux/compiler_types.h:568:38: error: call to '__compiletime_assert_462' declared with attribute error: BUILD_BUG_ON failed: bit > BITS_PER_TYPE(typeof_member(struct i915_pmu, enable)) - 1
> drivers/gpu/drm/i915/i915_pmu.c:116:3: note: in expansion of macro 'BUILD_BUG_ON'
>   116 |   BUILD_BUG_ON(bit >
> 
> As I understand it, the problem is that the function is not always fully
> inlined, but the __builtin_constant_p() can still evaluate the argument
> as being constant.
> 
> Marking it as __always_inline so far works for me in all configurations.
> 
> Fixes: a7137b1825b5 ("drm/i915/pmu: Fix build error with GCOV and AutoFDO enabled")
> Fixes: a644fde77ff7 ("drm/i915/pmu: Change bitmask of enabled events to u32")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpu/drm/i915/i915_pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index 990bfaba3ce4..5bc696bfbb0f 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.c
> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> @@ -108,7 +108,7 @@ static unsigned int config_bit(const u64 config)
>  		return other_bit(config);
>  }
>  
> -static u32 config_mask(const u64 config)
> +static __always_inline u32 config_mask(const u64 config)

hmm, it looks like the __builtin_constant_p() with BUILD_BUG_ON is a bit fragile
design down here. But this always_inline will enforce deterministic behavior
indeed.

So,
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

pushing to drm-intel-next right now as well...

>  {
>  	unsigned int bit = config_bit(config);
>  
> -- 
> 2.39.5
>