scsi: ilog2: create truly constant version for sparse

Sparse emits errors about ilog2() in array indices because of the use of
__ilog2_32() and __ilog2_64(), rightly so
(https://www.spinics.net/lists/linux-sparse/msg03471.html).

Create a const_ilog2() variant that works with sparse for this scenario.

(Note: checkpatch.pl complains about missing parentheses, but that
appears to be a false positive. I can get rid of the warning simply by
inserting whitespace, making checkpatch "see" the whole macro).

Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 24 insertions, 11 deletions

diff --git a/include/linux/log2.h b/include/linux/log2.h
index 41a1ae010993..2af7f77866d0 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -72,16 +72,13 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
 }
 
 /**
- * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value
+ * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value
  * @n: parameter
  *
- * constant-capable log of base 2 calculation
- * - this can be used to initialise global variables from constant data, hence
- * the massive ternary operator construction
- *
- * selects the appropriately-sized optimised version depending on sizeof(n)
+ * Use this where sparse expects a true constant expression, e.g. for array
+ * indices.
  */
-#define ilog2(n)                                \
+#define const_ilog2(n)                          \
 (                                               \
         __builtin_constant_p(n) ? (             \
                 (n) < 2 ? 0 :                   \
@@ -147,10 +144,26 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
                 (n) & (1ULL <<  4) ?  4 :       \
                 (n) & (1ULL <<  3) ?  3 :       \
                 (n) & (1ULL <<  2) ?  2 :       \
-                1 ) :                           \
-        (sizeof(n) <= 4) ?                      \
-        __ilog2_u32(n) :                        \
-        __ilog2_u64(n)                          \
+                1) :                            \
+        -1)
+
+/**
+ * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value
+ * @n: parameter
+ *
+ * constant-capable log of base 2 calculation
+ * - this can be used to initialise global variables from constant data, hence
+ * the massive ternary operator construction
+ *
+ * selects the appropriately-sized optimised version depending on sizeof(n)
+ */
+#define ilog2(n) \
+( \
+        __builtin_constant_p(n) ?       \
+        const_ilog2(n) :                \
+        (sizeof(n) <= 4) ?              \
+        __ilog2_u32(n) :                \
+        __ilog2_u64(n)                  \
  )
 
 /**