linux-kernel - Re: [PATCH v2 3/4] clk: samsung: clk-pll: Add support for pll

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Message-ID: <a82340ab-a1db-4089-a804-acf9882782f4@suswa.mountain>
Date: Fri, 19 Jul 2024 13:48:21 -0500
From: Dan Carpenter <dan.carpenter@...aro.org>
To: oe-kbuild@...ts.linux.dev, Sunyeal Hong <sunyeal.hong@...sung.com>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>
Cc: lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
	linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Sunyeal Hong <sunyeal.hong@...sung.com>
Subject: Re: [PATCH v2 3/4] clk: samsung: clk-pll: Add support for pll_531x

Hi Sunyeal,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Sunyeal-Hong/dt-bindings-clock-add-Exynos-Auto-v920-SoC-CMU-bindings/20240708-072150
base:   https://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux.git for-next
patch link:    https://lore.kernel.org/r/20240707231331.3433340-4-sunyeal.hong%40samsung.com
patch subject: [PATCH v2 3/4] clk: samsung: clk-pll: Add support for pll_531x
config: arc-randconfig-r071-20240719 (https://download.01.org/0day-ci/archive/20240720/202407200028.5AADGhmj-lkp@intel.com/config)
compiler: arc-elf-gcc (GCC) 13.2.0

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>
| Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
| Closes: https://lore.kernel.org/r/202407200028.5AADGhmj-lkp@intel.com/

smatch warnings:
drivers/clk/samsung/clk-pll.c:1292 samsung_pll531x_recalc_rate() warn: mask and shift to zero: expr='fdiv >> 31'

vim +1292 drivers/clk/samsung/clk-pll.c

5c788df7a25de7 Sunyeal Hong 2024-07-08  1277  static unsigned long samsung_pll531x_recalc_rate(struct clk_hw *hw,
5c788df7a25de7 Sunyeal Hong 2024-07-08  1278  						 unsigned long parent_rate)
5c788df7a25de7 Sunyeal Hong 2024-07-08  1279  {
5c788df7a25de7 Sunyeal Hong 2024-07-08  1280  	struct samsung_clk_pll *pll = to_clk_pll(hw);
5c788df7a25de7 Sunyeal Hong 2024-07-08  1281  	u32 mdiv, pdiv, sdiv, pll_con0, pll_con8;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1282  	s32 fdiv;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1283  	u64 fout = parent_rate;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1284  
5c788df7a25de7 Sunyeal Hong 2024-07-08  1285  	pll_con0 = readl_relaxed(pll->con_reg);
5c788df7a25de7 Sunyeal Hong 2024-07-08  1286  	pll_con8 = readl_relaxed(pll->con_reg + 20);
5c788df7a25de7 Sunyeal Hong 2024-07-08  1287  	mdiv = (pll_con0 >> PLL531X_MDIV_SHIFT) & PLL531X_MDIV_MASK;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1288  	pdiv = (pll_con0 >> PLL531X_PDIV_SHIFT) & PLL531X_PDIV_MASK;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1289  	sdiv = (pll_con0 >> PLL531X_SDIV_SHIFT) & PLL531X_SDIV_MASK;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1290  	fdiv = (s32)(pll_con8 & PLL531X_FDIV_MASK);

PLL531X_FDIV_MASK is 0xffff.  Was this supposed to be a cast to s16
instead of s32?  Why is fdiv signed?  Shifting negative values is
undefined in C.

5c788df7a25de7 Sunyeal Hong 2024-07-08  1291  
5c788df7a25de7 Sunyeal Hong 2024-07-08 @1292  	if (fdiv >> 31)

It's really unclear what's happening here.  If I had to guess, I'd say
that this was testing to see if fdiv was negative.

5c788df7a25de7 Sunyeal Hong 2024-07-08  1293  		mdiv--;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1294  
5c788df7a25de7 Sunyeal Hong 2024-07-08  1295  	fout *= ((u64)mdiv << 24) + (fdiv >> 8);
                                                                             ^^^^^^^^^
More shifting.

5c788df7a25de7 Sunyeal Hong 2024-07-08  1296  	do_div(fout, (pdiv << sdiv));
5c788df7a25de7 Sunyeal Hong 2024-07-08  1297  	fout >>= 24;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1298  
5c788df7a25de7 Sunyeal Hong 2024-07-08  1299  	return (unsigned long)fout;
5c788df7a25de7 Sunyeal Hong 2024-07-08  1300  }

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki