linux-kernel - Re: drivers/media/i2c/tc358746.c:817:13: warning: 'p

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Date:   Fri, 24 Feb 2023 09:45:59 +0100
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     kernel test robot <lkp@...el.com>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: drivers/media/i2c/tc358746.c:817:13: warning: 'p_best' is used
 uninitialized

On 23-02-24, kernel test robot wrote:
> Hi Marco,
> 
> FYI, the error/warning still remains.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   e4bc15889506723d7b93c053ad4a75cd58248d74
> commit: 80a21da360516fa602f3a50eb9792f9dfbfb5fdb media: tc358746: add Toshiba TC358746 Parallel to CSI-2 bridge driver
> date:   4 months ago
> config: arc-randconfig-r031-20230223 (https://download.01.org/0day-ci/archive/20230224/202302240951.roaFGUy5-lkp@intel.com/config)
> compiler: arceb-elf-gcc (GCC) 12.1.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=80a21da360516fa602f3a50eb9792f9dfbfb5fdb
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 80a21da360516fa602f3a50eb9792f9dfbfb5fdb
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arc olddefconfig
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arc SHELL=/bin/bash drivers/media/i2c/

This is still a false positive, should we initialize p_best to make the
compiler happy? I think Hans did this once, but he said that this will
be gone with gcc-13 if I remember correctly.

Regards,
  Marco

> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@...el.com>
> | Link: https://lore.kernel.org/oe-kbuild-all/202302240951.roaFGUy5-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    drivers/media/i2c/tc358746.c: In function 'tc358746_find_pll_settings':
> >> drivers/media/i2c/tc358746.c:817:13: warning: 'p_best' is used uninitialized [-Wuninitialized]
>      817 |         u16 p_best, p;
>          |             ^~~~~~
> >> drivers/media/i2c/tc358746.c:816:13: warning: 'm_best' is used uninitialized [-Wuninitialized]
>      816 |         u16 m_best, mul;
>          |             ^~~~~~
> 
> 
> vim +/p_best +817 drivers/media/i2c/tc358746.c
> 
>    805	
>    806	static unsigned long tc358746_find_pll_settings(struct tc358746 *tc358746,
>    807							unsigned long refclk,
>    808							unsigned long fout)
>    809	
>    810	{
>    811		struct device *dev = tc358746->sd.dev;
>    812		unsigned long best_freq = 0;
>    813		u32 min_delta = 0xffffffff;
>    814		u16 prediv_max = 17;
>    815		u16 prediv_min = 1;
>  > 816		u16 m_best, mul;
>  > 817		u16 p_best, p;
>    818		u8 postdiv;
>    819	
>    820		if (fout > 1000 * HZ_PER_MHZ) {
>    821			dev_err(dev, "HS-Clock above 1 Ghz are not supported\n");
>    822			return 0;
>    823		}
>    824	
>    825		if (fout >= 500 * HZ_PER_MHZ)
>    826			postdiv = 1;
>    827		else if (fout >= 250 * HZ_PER_MHZ)
>    828			postdiv = 2;
>    829		else if (fout >= 125 * HZ_PER_MHZ)
>    830			postdiv = 4;
>    831		else
>    832			postdiv = 8;
>    833	
>    834		for (p = prediv_min; p <= prediv_max; p++) {
>    835			unsigned long delta, fin;
>    836			u64 tmp;
>    837	
>    838			fin = DIV_ROUND_CLOSEST(refclk, p);
>    839			if (fin < 4 * HZ_PER_MHZ || fin > 40 * HZ_PER_MHZ)
>    840				continue;
>    841	
>    842			tmp = fout * p * postdiv;
>    843			do_div(tmp, fin);
>    844			mul = tmp;
>    845			if (mul > 511)
>    846				continue;
>    847	
>    848			tmp = mul * fin;
>    849			do_div(tmp, p * postdiv);
>    850	
>    851			delta = abs(fout - tmp);
>    852			if (delta < min_delta) {
>    853				p_best = p;
>    854				m_best = mul;
>    855				min_delta = delta;
>    856				best_freq = tmp;
>    857			};
>    858	
>    859			if (delta == 0)
>    860				break;
>    861		};
>    862	
>    863		if (!best_freq) {
>    864			dev_err(dev, "Failed find PLL frequency\n");
>    865			return 0;
>    866		}
>    867	
>    868		tc358746->pll_post_div = postdiv;
>    869		tc358746->pll_pre_div = p_best;
>    870		tc358746->pll_mul = m_best;
>    871	
>    872		if (best_freq != fout)
>    873			dev_warn(dev, "Request PLL freq:%lu, found PLL freq:%lu\n",
>    874				 fout, best_freq);
>    875	
>    876		dev_dbg(dev, "Found PLL settings: freq:%lu prediv:%u multi:%u postdiv:%u\n",
>    877			best_freq, p_best, m_best, postdiv);
>    878	
>    879		return best_freq;
>    880	}
>    881	
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests
>