Re: [PATCH v3 1/3] drm/i915: introduce REG_BIT() and REG_GENMASK() to define register contents

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On Wed, 27 Feb 2019 18:02:36 +0100, Jani Nikula <jani.nikula@xxxxxxxxx> wrote:

@@ -116,6 +116,34 @@
  *  #define GEN8_BAR                    _MMIO(0xb888)
  */
+/**
+ * REG_BIT() - Prepare a u32 bit value
+ * @__n: 0-based bit number
+ *
+ * Local wrapper for BIT() to force u32, with compile time checks.
+ *
+ * @return: Value with bit @__n set.
+ */
+#define REG_BIT(__n)							\
+	((u32)(BIT(__n) +						\
+	       BUILD_BUG_ON_ZERO(__builtin_constant_p(__n) &&		\
+				 ((__n) < 0 || (__n) > 31))))

Maybe to simplify the code we can define this macro using macro below:

#define REG_BIT(__n) REG_GENMASK(__n, __n)

+
+/**
+ * REG_GENMASK() - Prepare a continuous u32 bitmask
+ * @__high: 0-based high bit
+ * @__low: 0-based low bit
+ *
+ * Local wrapper for GENMASK() to force u32, with compile time checks.
+ *
+ * @return: Continuous bitmask from @__high to @__low, inclusive.
+ */
+#define REG_GENMASK(__high, __low)					\
+	((u32)(GENMASK(__high, __low) +					\
+	       BUILD_BUG_ON_ZERO(__builtin_constant_p(__high) &&	\
+				 __builtin_constant_p(__low) &&		\
+				 ((__low) < 0 || (__high) > 31 || (__low) > (__high)))))
+

nit: Since we are defining new set of macros, do we really have to follow
naming of the underlying macros? maybe we can can have clear new names:

	REG_BIT(n)
	REG_BITS(hi,low)

Thanks,
Michal

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