On Fri, Jan 27, 2017 at 05:57:06PM +0200, Jani Nikula wrote:
> This allows the use of more than 3 ports/pipes/whatever without tricks,
> even if the register offsets are not evenly spaced.
>
> There's the risk of out of bounds access if we're not careful; currently
> that would "just" lead to the wrong register offset being used. It might
> be possible to add build bug ons for build time constant indexing.
>
> We already have ports defined up to E, not sure if we might have bugs
> related to them and the current _PORT3() macro.
>
> text data bss dec hex filename
> 1239868 46199 4096 1290163 13afb3 drivers/gpu/drm/i915/i915.ko
> 1238828 46199 4096 1289123 13aba3 drivers/gpu/drm/i915/i915.ko
>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tursulin@xxxxxxxxxxx>
> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_reg.h | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 672cb102f477..c6435a447300 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -48,6 +48,8 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
> return !i915_mmio_reg_equal(reg, INVALID_MMIO_REG);
> }
>
> +#define _PICK(__index, ...) (((const u32 []){ __VA_ARGS__ })[__index])
Very neat. The danger is that for a variable index, the compiler will
plonk the array on the stack, for each invocation. Though for a constant
the compiler will see through it and generate the right constant.
https://godbolt.org/g/YCK1od
Given that it looks like the compiler will get smarter, this looks like
a much less error prone way of writing these.
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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