linux-kernel - Re: [PATCH] firewire: core: suppress overflow warning when computing jiffies from isochronous cycle

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Message-ID: <20250925135321.GA329042@workstation.local>
Date: Thu, 25 Sep 2025 22:53:21 +0900
From: Takashi Sakamoto <o-takashi@...amocchi.jp>
To: linux1394-devel@...ts.sourceforge.net
Cc: linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] firewire: core: suppress overflow warning when computing
 jiffies from isochronous cycle

On Wed, Sep 24, 2025 at 10:11:40PM +0900, Takashi Sakamoto wrote:
> 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@...el.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")
> Signed-off-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
> ---
>  drivers/firewire/core.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied to for-next branch.


Regards

Takashi Sakamoto