[Intel-gfx] [PATCH] drm/i915: make REG_BIT() and REG_GENMASK() work with variables

[Chris Wilson]

Quoting Jani Nikula (2019-05-24 19:52:53)
> REG_BIT() and REG_GENMASK() were intended to work with both constant
> expressions and otherwise, with the former having extra compile time
> checks for the bit ranges. Incredibly, the result of
> __builtin_constant_p() is not an integer constant expression when given
> a non-constant expression, leading to errors in BUILD_BUG_ON_ZERO().
> 
> Replace __builtin_constant_p() with the __is_constexpr() magic spell.
> 
> Reported-by: Ville Syrjala <ville.syrjala at linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 49dce04dd688..019c48748dc9 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -126,7 +126,7 @@
>   */
>  #define REG_BIT(__n)                                                   \
>         ((u32)(BIT(__n) +                                               \
> -              BUILD_BUG_ON_ZERO(__builtin_constant_p(__n) &&           \
> +              BUILD_BUG_ON_ZERO(__is_constexpr(__n) &&         \
>                                  ((__n) < 0 || (__n) > 31))))
>  
>  /**
> @@ -140,8 +140,8 @@
>   */
>  #define REG_GENMASK(__high, __low)                                     \
>         ((u32)(GENMASK(__high, __low) +                                 \
> -              BUILD_BUG_ON_ZERO(__builtin_constant_p(__high) &&        \
> -                                __builtin_constant_p(__low) &&         \
> +              BUILD_BUG_ON_ZERO(__is_constexpr(__high) &&      \
> +                                __is_constexpr(__low) &&               \
>                                  ((__low) < 0 || (__high) > 31 || (__low) > (__high)))))

Ok, one old one remaining in _MASKED_FIELD().

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris