From: Arnd Bergmann arnd@arndb.de
Randconfig builds on 32-bit machines show lots of warnings for the i915 driver for incorrect bit masks like:
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:2584:9: error: shift count >= width of type [-Werror,-Wshift-count-overflow] return hweight64(VDBOX_MASK(&i915->gt)); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/asm-generic/bitops/const_hweight.h:29:49: note: expanded from macro 'hweight64' #define hweight64(w) (__builtin_constant_p(w) ? __const_hweight64(w) : __arch_hweight64(w))
Since this is a 64-bit mask, use GENMASK_ULL instead of GENMASK.
Signed-off-by: Arnd Bergmann arnd@arndb.de --- drivers/gpu/drm/i915/i915_drv.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index 0a3ee4f9dc0a..ca32fa0d6a57 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -1624,7 +1624,7 @@ tgl_revids_get(struct drm_i915_private *dev_priv) unsigned int first__ = (first); \ unsigned int count__ = (count); \ ((gt)->info.engine_mask & \ - GENMASK(first__ + count__ - 1, first__)) >> first__; \ + GENMASK_ULL(first__ + count__ - 1, first__)) >> first__; \ }) #define VDBOX_MASK(gt) \ ENGINE_INSTANCES_MASK(gt, VCS0, I915_MAX_VCS)
Quoting Arnd Bergmann (2020-12-30 15:39:14)
mask is a u8.
VCS0 is 2, I915_MAX_VCS 4
(u8 & GENMASK(5, 2)) >> 2
So it's upset by hweight64() on the unsigned long? So hweight_long?
Or use a cast, hweight8((intel_engine_mask_t)VDMASK())?
static __always_inline int engine_count(intel_engine_mask_t mask) { return sizeof(mask) == 1 ? hweight8(mask) : sizeof(mask) == 2 ? hweight16(mask) : sizeof(mask) == 4 ? hweight32(mask) : hweight64(mask); } -Chris
On Wed, Dec 30, 2020 at 4:56 PM Chris Wilson chris@chris-wilson.co.uk wrote:
Ah right, I misread the warning then.
I suspect what is going on is that clang once again warns because it performs more code checks before dead-code elimination than gcc does. The warning is for the __const_hweight64() case, which is not actually used here because the input is not a compile-time constant.
So hweight_long?
That seems to work, I'll send a new version with that.
Fine with me as well. If you prefer that way, I'll let you handle that.
Arnd
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