On Fri, 20 Jan 2023, Lucas De Marchi <lucas.demarchi@xxxxxxxxx> wrote:
> 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
Would be interesting to see what this does, and whether the compiler has
the smarts to combine these within each file:
-#define _PICK(__index, ...) (((const u32 []){ __VA_ARGS__ })[__index])
+#define _PICK(__index, ...) (((static const u32 []){ __VA_ARGS__ })[__index])
> 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@xxxxxxxxx>
> ---
> 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::
I'd like this to be clear about which range is used for index ==
__c_index, instead of saying "below" and "above".
No need for the double colon :: because this isn't a kernel-doc comment.
> + *
> + * #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, \
The example uses a different name for the macro.
> + * _FOO_A, _FOO_B, \
> + * _SUPER_FOO_A, _SUPER_FOO_B))
> + *
> + * This expands to:
> + * 0: 0xf000,
> + * 1: 0xf004,
> + * 2: 0xf008,
> + * 3: 0xa100,
With the above definitions, this would be 3: 0xa000.
> + * 4: 0xa200,
> + * 5: 0xa300,
> + * ...
> + */
> +#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.
> *
--
Jani Nikula, Intel Open Source Graphics Center
