Re: [PATCH v2 3/4] clk: samsung: clk-pll: Add support for pll_531x

Dan Carpenter
2024-07-19T18:48:24Z

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@intel.com>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.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 }

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