linux-kernel - drivers/gpu/drm/bridge/imx/imx93-mipi-dsi.c:230:26: warning: 'best

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Date:   Wed, 15 Nov 2023 17:12:44 +0800
From:   kernel test robot <lkp@...el.com>
To:     Liu Ying <victor.liu@....com>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Robert Foss <rfoss@...nel.org>
Subject: drivers/gpu/drm/bridge/imx/imx93-mipi-dsi.c:230:26: warning:
 'best_m' is used uninitialized

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   c42d9eeef8e5ba9292eda36fd8e3c11f35ee065c
commit: ce62f8ea7e3f8a8e788c3b5ea0195f1224575b66 drm/bridge: imx: Add i.MX93 MIPI DSI support
date:   4 weeks ago
config: arc-randconfig-001-20231115 (https://download.01.org/0day-ci/archive/20231115/202311151746.f7u7dzbZ-lkp@intel.com/config)
compiler: arceb-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231115/202311151746.f7u7dzbZ-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/202311151746.f7u7dzbZ-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/gpu/drm/bridge/imx/imx93-mipi-dsi.c: In function 'dphy_pll_get_configure_from_opts.isra':
>> drivers/gpu/drm/bridge/imx/imx93-mipi-dsi.c:230:26: warning: 'best_m' is used uninitialized [-Wuninitialized]
     230 |         unsigned long m, best_m;
         |                          ^~~~~~
>> drivers/gpu/drm/bridge/imx/imx93-mipi-dsi.c:229:39: warning: 'best_n' is used uninitialized [-Wuninitialized]
     229 |         unsigned int min_n, max_n, n, best_n;
         |                                       ^~~~~~


vim +/best_m +230 drivers/gpu/drm/bridge/imx/imx93-mipi-dsi.c

   218	
   219	static int
   220	dphy_pll_get_configure_from_opts(struct imx93_dsi *dsi,
   221					 struct phy_configure_opts_mipi_dphy *dphy_opts,
   222					 struct dphy_pll_cfg *cfg)
   223	{
   224		struct device *dev = dsi->dev;
   225		unsigned long fin = dsi->ref_clk_rate;
   226		unsigned long fout;
   227		unsigned long best_fout = 0;
   228		unsigned int fvco_div;
 > 229		unsigned int min_n, max_n, n, best_n;
 > 230		unsigned long m, best_m;
   231		unsigned long min_delta = ULONG_MAX;
   232		unsigned long delta;
   233		u64 tmp;
   234	
   235		if (dphy_opts->hs_clk_rate < DATA_RATE_MIN_SPEED ||
   236		    dphy_opts->hs_clk_rate > DATA_RATE_MAX_SPEED) {
   237			dev_dbg(dev, "invalid data rate per lane: %lu\n",
   238				dphy_opts->hs_clk_rate);
   239			return -EINVAL;
   240		}
   241	
   242		fout = data_rate_to_fout(dphy_opts->hs_clk_rate);
   243	
   244		/* DPHY Databook 3.3.6.1 Output Frequency */
   245		/* Fout = Fvco / Fvco_div = (Fin * M) / (Fvco_div * N) */
   246		/* Fvco_div could be 1/2/4/8 according to Fout range. */
   247		fvco_div = 8UL / min(DIV_ROUND_UP(fout, FVCO_DIV_FACTOR), 8UL);
   248	
   249		/* limitation: 2MHz <= Fin / N <= 8MHz */
   250		min_n = DIV_ROUND_UP_ULL((u64)fin, MHZ(8));
   251		max_n = DIV_ROUND_DOWN_ULL((u64)fin, MHZ(2));
   252	
   253		/* clamp possible N(s) */
   254		min_n = clamp(min_n, N_MIN, N_MAX);
   255		max_n = clamp(max_n, N_MIN, N_MAX);
   256	
   257		dev_dbg(dev, "Fout = %lu, Fvco_div = %u, n_range = [%u, %u]\n",
   258			fout, fvco_div, min_n, max_n);
   259	
   260		for (n = min_n; n <= max_n; n++) {
   261			/* M = (Fout * N * Fvco_div) / Fin */
   262			m = DIV_ROUND_CLOSEST(fout * n * fvco_div, fin);
   263	
   264			/* check M range */
   265			if (m < M_MIN || m > M_MAX)
   266				continue;
   267	
   268			/* calculate temporary Fout */
   269			tmp = m * fin;
   270			do_div(tmp, n * fvco_div);
   271			if (tmp < FOUT_MIN || tmp > FOUT_MAX)
   272				continue;
   273	
   274			delta = abs(fout - tmp);
   275			if (delta < min_delta) {
   276				best_n = n;
   277				best_m = m;
   278				min_delta = delta;
   279				best_fout = tmp;
   280			}
   281		}
   282	
   283		if (best_fout) {
   284			cfg->m = best_m;
   285			cfg->n = best_n;
   286			dev_dbg(dev, "best Fout = %lu, m = %u, n = %u\n",
   287				best_fout, cfg->m, cfg->n);
   288		} else {
   289			dev_dbg(dev, "failed to find best Fout\n");
   290			return -EINVAL;
   291		}
   292	
   293		return 0;
   294	}
   295	

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