Re: [PATCH] drm/i915: protect macro parameters in SWING_SEL_{UPP, LO}WER

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 23 Mar 2018, Paulo Zanoni <paulo.r.zanoni@intel.com> wrote:
> Protect the macro parameters with parens in order to avoid priority
> issues on macro evaluation when the macro argument is not a single
> operand.
>
> This is not a problem today, but it could be in the future. I found
> this while reviewing a patch that introduces new callers for the
> macros.
>
> Reference: commit 04416108ccea ("drm/i915/cnl: Add registers related to voltage swing sequences.")
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index da2f6c623ab2..49c90e1aa796 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -1729,9 +1729,9 @@ enum i915_power_well_id {
>  
>  #define CNL_PORT_TX_DW2_GRP(port)	_MMIO(_CNL_PORT_TX_DW_GRP((port), 2))
>  #define CNL_PORT_TX_DW2_LN0(port)	_MMIO(_CNL_PORT_TX_DW_LN0((port), 2))
> -#define   SWING_SEL_UPPER(x)		((x >> 3) << 15)
> +#define   SWING_SEL_UPPER(x)		(((x) >> 3) << 15)
>  #define   SWING_SEL_UPPER_MASK		(1 << 15)
> -#define   SWING_SEL_LOWER(x)		((x & 0x7) << 11)
> +#define   SWING_SEL_LOWER(x)		(((x) & 0x7) << 11)

Unrelated to the patch at hand, but why do we have >> 3 and & 7 here
like this? We could have a single SWING_SEL_MASK() and SWING_SEL() that
would do the split to two parts. For future follow-up...

BR,
Jani.


>  #define   SWING_SEL_LOWER_MASK		(0x7 << 11)
>  #define   RCOMP_SCALAR(x)		((x) << 0)
>  #define   RCOMP_SCALAR_MASK		(0xFF << 0)

-- 
Jani Nikula, Intel Open Source Technology Center
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