Re: [PATCH v9 07/11] media: i2c: ov772x: Support frame interval handling

[kbuild test robot]

Hi Jacopo,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linuxtv-media/master]
[also build test WARNING on v4.16-rc2 next-20180220]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Jacopo-Mondi/Renesas-Capture-Engine-Unit-CEU-V4L2-driver/20180220-101027
base:   git://linuxtv.org/media_tree.git master
config: i386-allmodconfig (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   drivers/media/i2c/ov772x.c: In function 'ov772x_set_frame_rate.isra.2':
>> drivers/media/i2c/ov772x.c:643:7: warning: 'fsize' may be used uninitialized in this function [-Wmaybe-uninitialized]
     pclk = fps * fsize;
     ~~~~~^~~~~~~~~~~~~

vim +/fsize +643 drivers/media/i2c/ov772x.c

   604	
   605	static int ov772x_set_frame_rate(struct ov772x_priv *priv,
   606					 struct v4l2_fract *tpf,
   607					 const struct ov772x_color_format *cfmt,
   608					 const struct ov772x_win_size *win)
   609	{
   610		struct i2c_client *client = v4l2_get_subdevdata(&priv->subdev);
   611		unsigned long fin = clk_get_rate(priv->clk);
   612		unsigned int fps = tpf->numerator ?
   613				   tpf->denominator / tpf->numerator :
   614				   tpf->denominator;
   615		unsigned int best_diff;
   616		unsigned int fsize;
   617		unsigned int pclk;
   618		unsigned int diff;
   619		unsigned int idx;
   620		unsigned int i;
   621		u8 clkrc = 0;
   622		u8 com4 = 0;
   623		int ret;
   624	
   625		/* Approximate to the closest supported frame interval. */
   626		best_diff = ~0L;
   627		for (i = 0, idx = 0; i < OV772X_N_FRAME_INTERVALS; i++) {
   628			diff = abs(fps - ov772x_frame_intervals[i]);
   629			if (diff < best_diff) {
   630				idx = i;
   631				best_diff = diff;
   632			}
   633		}
   634		fps = ov772x_frame_intervals[idx];
   635	
   636		/* Use image size (with blankings) to calculate desired pixel clock. */
   637		if ((cfmt->com7 & OFMT_MASK) == OFMT_RGB ||
   638		    (cfmt->com7 & OFMT_MASK) == OFMT_YUV)
   639			fsize = win->sizeimage * 2;
   640		else if ((cfmt->com7 & OFMT_MASK) == OFMT_BRAW)
   641			fsize = win->sizeimage;
   642	
 > 643		pclk = fps * fsize;
   644	
   645		/*
   646		 * Pixel clock generation circuit is pretty simple:
   647		 *
   648		 * Fin -> [ / CLKRC_div] -> [ * PLL_mult] -> pclk
   649		 *
   650		 * Try to approximate the desired pixel clock testing all available
   651		 * PLL multipliers (1x, 4x, 6x, 8x) and calculate corresponding
   652		 * divisor with:
   653		 *
   654		 * div = PLL_mult * Fin / pclk
   655		 *
   656		 * and re-calculate the pixel clock using it:
   657		 *
   658		 * pclk = Fin * PLL_mult / CLKRC_div
   659		 *
   660		 * Choose the PLL_mult and CLKRC_div pair that gives a pixel clock
   661		 * closer to the desired one.
   662		 *
   663		 * The desired pixel clock is calculated using a known frame size
   664		 * (blanking included) and FPS.
   665		 */
   666		best_diff = ~0L;
   667		for (i = 0; i < ARRAY_SIZE(ov772x_pll); i++) {
   668			unsigned int pll_mult = ov772x_pll[i].mult;
   669			unsigned int pll_out = pll_mult * fin;
   670			unsigned int t_pclk;
   671			unsigned int div;
   672	
   673			if (pll_out < pclk)
   674				continue;
   675	
   676			div = DIV_ROUND_CLOSEST(pll_out, pclk);
   677			t_pclk = DIV_ROUND_CLOSEST(fin * pll_mult, div);
   678			diff = abs(pclk - t_pclk);
   679			if (diff < best_diff) {
   680				best_diff = diff;
   681				clkrc = CLKRC_DIV(div);
   682				com4 = ov772x_pll[i].com4;
   683			}
   684		}
   685	
   686		ret = ov772x_write(client, COM4, com4 | COM4_RESERVED);
   687		if (ret < 0)
   688			return ret;
   689	
   690		ret = ov772x_write(client, CLKRC, clkrc | CLKRC_RESERVED);
   691		if (ret < 0)
   692			return ret;
   693	
   694		tpf->numerator = 1;
   695		tpf->denominator = fps;
   696		priv->fps = tpf->denominator;
   697	
   698		return 0;
   699	}
   700	

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