firewire: core: suppress overflow warning when computing jiffies from isochronous...

The multiplication by USEC_PER_SEC (=1000000L) may trigger an overflow
warning with 32 bit storage. In the case of the subsystem the input value
ranges between 800 and 16000, thus the result always fits within 32 bit
storage.

This commit suppresses the warning by using widening conversion to 64 bit
storage before multiplication, then using narrowing conversion to 32 bit
storage.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202509170136.b5ZHaNAV-lkp@intel.com/
Fixes: 379b870c28c6 ("firewire: core: use helper macros instead of direct access to HZ")
Link: https://lore.kernel.org/r/20250924131140.261686-1-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

diff --git a/drivers/firewire/core.h b/drivers/firewire/core.h
index 7f2ca93406cedfa5412e1e72da455d2c40bb1491..2dd715a580ac8b448ad7feeb47cc70c71ef7a036 100644 (file)
--- a/drivers/firewire/core.h
+++ b/drivers/firewire/core.h
@@ -30,7 +30,7 @@ struct fw_packet;
 // This is the arbitrary value we use to indicate a mismatched gap count.
 #define GAP_COUNT_MISMATCHED   0
 
-#define isoc_cycles_to_jiffies(cycles) usecs_to_jiffies(cycles * USEC_PER_SEC / 8000)
+#define isoc_cycles_to_jiffies(cycles) usecs_to_jiffies((u32)((u64)(cycles) * USEC_PER_SEC / 8000))
 
 extern __printf(2, 3)
 void fw_err(const struct fw_card *card, const char *fmt, ...);