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

[Lucas De Marchi]

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>
---
 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