linux-kernel - RE: drivers/hid/intel-thc-hid/intel-thc/intel-thc-dma.c:298:38: sparse: sparse: dubious: !x

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Message-ID: <IA1PR11MB6098ECA558A36C0EAA1F21FCF4F72@IA1PR11MB6098.namprd11.prod.outlook.com>
Date: Wed, 5 Feb 2025 02:56:05 +0000
From: "Xu, Even" <even.xu@...el.com>
To: David Laight <david.laight.linux@...il.com>, lkp <lkp@...el.com>
CC: "oe-kbuild-all@...ts.linux.dev" <oe-kbuild-all@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Jiri Kosina
	<jikos@...nel.org>, "Sun, Xinpeng" <xinpeng.sun@...el.com>, "Srinivas
 Pandruvada" <srinivas.pandruvada@...ux.intel.com>, Mark Pearson
	<mpearson-lenovo@...ebb.ca>
Subject: RE: drivers/hid/intel-thc-hid/intel-thc/intel-thc-dma.c:298:38:
 sparse: sparse: dubious: !x | !y



> -----Original Message-----
> From: David Laight <david.laight.linux@...il.com>
> Sent: Thursday, January 30, 2025 6:22 AM
> To: lkp <lkp@...el.com>
> Cc: Xu, Even <even.xu@...el.com>; oe-kbuild-all@...ts.linux.dev; linux-
> kernel@...r.kernel.org; Jiri Kosina <jikos@...nel.org>; Sun, Xinpeng
> <xinpeng.sun@...el.com>; Srinivas Pandruvada
> <srinivas.pandruvada@...ux.intel.com>; Mark Pearson <mpearson-
> lenovo@...ebb.ca>
> Subject: Re: drivers/hid/intel-thc-hid/intel-thc/intel-thc-dma.c:298:38: sparse:
> sparse: dubious: !x | !y
> 
> On Wed, 29 Jan 2025 22:02:59 +0800
> kernel test robot <lkp@...el.com> wrote:
> 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   05dbaf8dd8bf537d4b4eb3115ab42a5fb40ff1f5
> > commit: a688404b2e20f00cce6d0a2b888ef4ca9154e144 HID: intel-thc-hid:
> intel-thc: Add THC DMA interfaces
> > date:   3 weeks ago
> > config: x86_64-allyesconfig
> > (https://download.01.org/0day-ci/archive/20250129/202501292144.eFDq4ov
> > r-lkp@...el.com/config)
> > compiler: gcc-12 (Debian 12.2.0-14) 12.2.0 reproduce (this is a W=1
> > build):
> > (https://download.01.org/0day-ci/archive/20250129/202501292144.eFDq4ov
> > r-lkp@...el.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new
> > version of the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@...el.com>
> > | Closes:
> > | https://lore.kernel.org/oe-kbuild-all/202501292144.eFDq4ovr-lkp@inte
> > | l.com/
> >
> > sparse warnings: (new ones prefixed by >>)
> > >> drivers/hid/intel-thc-hid/intel-thc/intel-thc-dma.c:298:38: sparse:
> > >> sparse: dubious: !x | !y
> >    drivers/hid/intel-thc-hid/intel-thc/intel-thc-dma.c: note: in included file
> (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/mm.h, ...):
> >    include/linux/page-flags.h:237:46: sparse: sparse: self-comparison always
> evaluates to false
> >    include/linux/page-flags.h:237:46: sparse: sparse: self-comparison
> > always evaluates to false
> >
> > vim +298 drivers/hid/intel-thc-hid/intel-thc/intel-thc-dma.c
> ...
> >    297		for (i = 0; i < config->prd_tbl_num; i++) {
> >  > 298			if (!config->sgls[i] | !config->sgls_nent[i])
> >    299				continue;
> ...
> 
> If zeros are unlikely the bit-wise 'or' is pretty likely to generate better code than a
> logical 'or'.
> 
> 	David

Good suggestion!
So the code can be optimized to:
	for (i = 0; i < config->prd_tbl_num; i++) {
	         if (config->sgls[i] && config->sgls_nent[i]) {
                                    ......
                       }
	}

Will create a patch for this.

Best Regards,
Even Xu