bits: introduce fixed-type BIT_U*()

Implement fixed-type BIT_U*() to help drivers add stricter checks,
like it was done for GENMASK_U*().

Signed-off-by: Lucas De Marchi <[email protected]>
Acked-by: Jani Nikula <[email protected]>
Co-developed-by: Vincent Mailhol <[email protected]>
Signed-off-by: Vincent Mailhol <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Yury Norov <[email protected]>

Author: lucasdemarchi

include/linux/bits.h

@@ -24,7 +24,7 @@
 /*
  * Missing asm support
  *
- * GENMASK_U*() depend on BITS_PER_TYPE() which relies on sizeof(),
+ * GENMASK_U*() and BIT_U*() depend on BITS_PER_TYPE() which relies on sizeof(),
  * something not available in asm. Nevertheless, fixed width integers is a C
  * concept. Assembly code can rely on the long and long long versions instead.
  */
@@ -55,6 +55,24 @@
 #define GENMASK_U32(h, l)	GENMASK_TYPE(u32, h, l)
 #define GENMASK_U64(h, l)	GENMASK_TYPE(u64, h, l)
 
+/*
+ * Fixed-type variants of BIT(), with additional checks like GENMASK_TYPE(). The
+ * following examples generate compiler warnings due to -Wshift-count-overflow:
+ *
+ * - BIT_U8(8)
+ * - BIT_U32(-1)
+ * - BIT_U32(40)
+ */
+#define BIT_INPUT_CHECK(type, nr) \
+	BUILD_BUG_ON_ZERO(const_true((nr) >= BITS_PER_TYPE(type)))
+
+#define BIT_TYPE(type, nr) ((type)(BIT_INPUT_CHECK(type, nr) + BIT_ULL(nr)))
+
+#define BIT_U8(nr)	BIT_TYPE(u8, nr)
+#define BIT_U16(nr)	BIT_TYPE(u16, nr)
+#define BIT_U32(nr)	BIT_TYPE(u32, nr)
+#define BIT_U64(nr)	BIT_TYPE(u64, nr)
+
 #else /* defined(__ASSEMBLY__) */
 
 /*