Re: [PATCH v2] drm/i915/pmu: Fix build error with GCOV and AutoFDO enabled

[Tvrtko Ursulin]

On 12/06/2025 09:30, Tzung-Bi Shih wrote:

i915_pmu.c may fail to build with GCOV and AutoFDO enabled.

../drivers/gpu/drm/i915/i915_pmu.c:116:3: error: call to 
'__compiletime_assert_487' declared with 'error' attribute: BUILD_BUG_ON failed: 
bit > BITS_PER_TYPE(typeof_member(struct i915_pmu, enable)) - 1
   116 |                 BUILD_BUG_ON(bit >
       |                 ^

Here is a way to reproduce the issue:
$ git checkout v6.15
$ mkdir build
$ ./scripts/kconfig/merge_config.sh -O build -n -m <(cat <<EOF
CONFIG_DRM=y
CONFIG_PCI=y
CONFIG_DRM_I915=y

CONFIG_PERF_EVENTS=y

CONFIG_DEBUG_FS=y
CONFIG_GCOV_KERNEL=y
CONFIG_GCOV_PROFILE_ALL=y

CONFIG_AUTOFDO_CLANG=y
EOF
)
$ PATH=${PATH}:${HOME}/llvm-20.1.5-x86_64/bin make LLVM=1 O=build \
        olddefconfig
$ PATH=${PATH}:${HOME}/llvm-20.1.5-x86_64/bin make LLVM=1 O=build \
        CLANG_AUTOFDO_PROFILE=...PATH_TO_SOME_AFDO_PROFILE... \
        drivers/gpu/drm/i915/i915_pmu.o

Although not super sure what happened, by reviewing the code, it should
depend on `__builtin_constant_p(bit)` directly instead of assuming
`__builtin_constant_p(config)` makes `bit` a builtin constant.

Also fix a nit, to reuse the `bit` local variable.

Fixes: a644fde77ff7 ("drm/i915/pmu: Change bitmask of enabled events to u32")
Reviewed-by: Nathan Chancellor <nat...@kernel.org>
Signed-off-by: Tzung-Bi Shih <tzun...@kernel.org>
---
Changes from v1:
(https://patchwork.freedesktop.org/patch/656115/?series=149617&rev=1)
- Collect R-b tag from Nathan.
- Rebase to v6.16-rc1.

LGTM. Pushed to drm-intel-gt-next, thank you!

Regards,

Tvrtko

  drivers/gpu/drm/i915/i915_pmu.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index e5a188ce3185..990bfaba3ce4 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -112,7 +112,7 @@ static u32 config_mask(const u64 config)
  {
        unsigned int bit = config_bit(config);

- if (__builtin_constant_p(config))

+       if (__builtin_constant_p(bit))
                BUILD_BUG_ON(bit >
                             BITS_PER_TYPE(typeof_member(struct i915_pmu,
                                                         enable)) - 1);
@@ -121,7 +121,7 @@ static u32 config_mask(const u64 config)
                             BITS_PER_TYPE(typeof_member(struct i915_pmu,
                                                         enable)) - 1);

- return BIT(config_bit(config));

+       return BIT(bit);
  }

static bool is_engine_event(struct perf_event *event)