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: <20250129222141.478c03df@pumpkin>
Date: Wed, 29 Jan 2025 22:21:41 +0000
From: David Laight <david.laight.linux@...il.com>
To: kernel test robot <lkp@...el.com>
Cc: Even Xu <even.xu@...el.com>, oe-kbuild-all@...ts.linux.dev,
 linux-kernel@...r.kernel.org, Jiri Kosina <jikos@...nel.org>, Xinpeng Sun
 <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.eFDq4ovr-lkp@intel.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.eFDq4ovr-lkp@intel.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@intel.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