gpu: nvgpu: posix: fix implementation of fls()

The POSIX implementation of fls() wasn't compliant with the Linux which
returns fls(0)=0 fls(1)=1, etc.

Bug found as result of JIRA NVGPU-1042.

Change-Id: Id0279e36332ffe236ed792c013c32f2da841f557
Signed-off-by: Philip Elcan <pelcan@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1828361
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: svc-misra-checker <svc-misra-checker@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Alex Waterman <alexw@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/drivers/gpu/nvgpu/os/posix/bitmap.c b/drivers/gpu/nvgpu/os/posix/bitmap.c
index f25f6e64..99ba62c3 100644
--- a/drivers/gpu/nvgpu/os/posix/bitmap.c
+++ b/drivers/gpu/nvgpu/os/posix/bitmap.c
@@ -37,7 +37,18 @@ unsigned long __nvgpu_posix_ffs(unsigned long word)
 
 unsigned long __nvgpu_posix_fls(unsigned long word)
 {
-        return ((sizeof(unsigned long) * 8UL) - 1UL) - __builtin_clzl(word);
+        unsigned long ret;
+
+        if (word == 0UL) {
+                /* __builtin_clzl() below is undefined for 0, so we have
+                 * to handle that as a special case.
+                 */
+                ret = 0UL;
+        } else {
+                ret = (sizeof(unsigned long) * 8UL) - __builtin_clzl(word);
+        }
+
+        return ret;
 }
 
 static unsigned long __find_next_bit(const unsigned long *addr,