[Intel-gfx] [PATCH v2 1/8] drm/i915: Add _PICK_EVEN_2RANGES()

[Srivatsa, Anusha]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Lucas
> De Marchi
> Sent: Friday, January 20, 2023 11:35 AM
> To: intel-gfx at lists.freedesktop.org
> Cc: De Marchi, Lucas <lucas.demarchi at intel.com>; dri-
> devel at lists.freedesktop.org
> Subject: [Intel-gfx] [PATCH v2 1/8] 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.
>
> Signed-off-by: Lucas De Marchi <lucas.demarchi 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..b7ec87464d69 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: 0xa100,
You mean 3:0xa000

> + *   4: 0xa200,
4:0xa100

> + *   5: 0xa300,
5:0xa200

Anusha
> + *   ...
> + */
> +#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