[Intel-gfx] [PATCH v2.1] drm/i915: Add _PICK_EVEN_2RANGES()

[Srivatsa, Anusha]

> -----Original Message-----
> From: De Marchi, Lucas <lucas.demarchi at intel.com>
> Sent: Monday, January 23, 2023 9:16 AM
> To: intel-gfx at lists.freedesktop.org; dri-devel at lists.freedesktop.org
> Cc: Srivatsa, Anusha <anusha.srivatsa at intel.com>; Jani Nikula
> <jani.nikula at linux.intel.com>; De Marchi, Lucas <lucas.demarchi at intel.com>
> Subject: [PATCH v2.1] drm/i915: Add _PICK_EVEN_2RANGES()
> 
> It's a constant pattern in the driver to need to use 2 ranges of MMIOs based on
> port, phy, pll, etc. When that happens, instead of using _PICK_EVEN(), _PICK()
> needs to be used.  Using _PICK() is discouraged due to some reasons like:
> 
> 1) It increases the code size since the array is declared
>    in each call site
> 2) Developers need to be careful not to incur an
>    out-of-bounds array access
> 3) Developers need to be careful that the indexes match the
>    table. For that it may be that the table needs to contain
>    holes, making (1) even worse.
> 
> Add a variant of _PICK_EVEN() that works with 2 ranges and selects which one
> to use depending on the index value.
> 
> v2: Fix the address expansion in the  example (Anusha)
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa at intel.com>

> ---
>  drivers/gpu/drm/i915/i915_reg_defs.h | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_reg_defs.h
> b/drivers/gpu/drm/i915/i915_reg_defs.h
> index be43580a6979..bab6a9ec2ddd 100644
> --- a/drivers/gpu/drm/i915/i915_reg_defs.h
> +++ b/drivers/gpu/drm/i915/i915_reg_defs.h
> @@ -119,6 +119,34 @@
>   */
>  #define _PICK_EVEN(__index, __a, __b) ((__a) + (__index) * ((__b) - (__a)))
> 
> +/*
> + * Like _PICK_EVEN(), but supports 2 ranges of evenly spaced address offsets.
> + * The first range is used for indexes below @__c_index, and the second
> + * range is used for anything above it. Example::
> + *
> + * #define _FOO_A			0xf000
> + * #define _FOO_B			0xf004
> + * #define _FOO_C			0xf008
> + * #define _SUPER_FOO_A			0xa000
> + * #define _SUPER_FOO_B			0xa100
> + * #define FOO(x)			_MMIO(_PICK_EVEN_RANGES(x, 3,
> 		\
> + *					      _FOO_A, _FOO_B,
> 	\
> + *					      _SUPER_FOO_A, _SUPER_FOO_B))
> + *
> + * This expands to:
> + *	0: 0xf000,
> + *	1: 0xf004,
> + *	2: 0xf008,
> + *	3: 0xa000,
> + *	4: 0xa100,
> + *	5: 0xa200,
> + *	...
> + */
> +#define _PICK_EVEN_2RANGES(__index, __c_index, __a, __b, __c, __d)
> 	\
> +	(BUILD_BUG_ON_ZERO(!__is_constexpr(__c_index)) +
> 	\
> +	 ((__index) < (__c_index) ? _PICK_EVEN(__index, __a, __b) :
> 	\
> +				   _PICK_EVEN((__index) - (__c_index), __c,
> __d)))
> +
>  /*
>   * Given the arbitrary numbers in varargs, pick the 0-based __index'th number.
>   *
> --
> 2.39.0