[IMX6Q][Android4.4] LCD参数匹配过程分析

Platform: IMX6Q

OS: Android 4.4

本文只讨论lvds接口的是lcd参数匹配的过程，mipi dsi以及其他接口部分会有一点差异。

核心函数fb_find_mode()，在分析之前先了解下几个参数。

重要参数说明：

1. ldb.c中的 ldb_modedb

static struct fb_videomode ldb_modedb[] = {
    {
     "LDB-WXGA", 60, 1280, 800, 14065,
     40, 40,
     10, 3,
     80, 10,
     0,
     FB_VMODE_NONINTERLACED,
     FB_MODE_IS_DETAILED,},
    {
     "LDB-XGA", 60, 1024, 768, 15385,
     220, 40,
     21, 7,
     60, 10,
     0,
     FB_VMODE_NONINTERLACED,
     FB_MODE_IS_DETAILED,},
    {
     "LDB-1080P60", 60, 1920, 1080, 7692,
     100, 40,
     30, 3,
     10, 2,
     0,
     FB_VMODE_NONINTERLACED,
     FB_MODE_IS_DETAILED,},
     {
     "LDB-WSVGA", //Name
     60, //refresh
     1024, //xres
     600, //yres
     19531,//pixclock
     220, 40,//left/right margin
     21, 7,//upper/lower margin
     60, 7,//hsync_len,vsync_len
     0,//sync
     FB_VMODE_NONINTERLACED,//vmode
     FB_MODE_IS_DETAILED,},
};
static int ldb_modedb_sz = ARRAY_SIZE(ldb_modedb);

系统lvds接口支持的lcd时序参数都在此了。

2. board-mx6-xxx.c中的ipuv3_fb_platform_data结构

本例是：

static struct ipuv3_fb_platform_data tek_fb_data[] = {
    { /*fb0*/
    .disp_dev = "ldb",
    .interface_pix_fmt = IPU_PIX_FMT_RGB24,
    .mode_str = "LDB-WSVGA",
    .default_bpp = 32,
    .int_clk = false,
    .late_init = false,
    }, {
    .disp_dev = "hdmi",
    .interface_pix_fmt = IPU_PIX_FMT_RGB24,
    .mode_str = "1920x1080M@60",
    .default_bpp = 32,
    .int_clk = false,
    .late_init = false,
    },
    {
    .disp_dev = "lcd",
    .interface_pix_fmt = IPU_PIX_FMT_RGB565,
    .mode_str = "CLAA-WVGA",
    .default_bpp = 16,
    .int_clk = false,
    .late_init = false,
    }, {
    .disp_dev = "ldb",
    .interface_pix_fmt = IPU_PIX_FMT_RGB666,
    .mode_str = "LDB-VGA",
    .default_bpp = 16,
    .int_clk = false,
    .late_init = false,
    },
};

fb_find_mode()用到其mode_str里的值去ldb_modedb查找有没有对应lcd时序参数。

此mode_str其实就是后面会提到的mode_options, 格式如下：

  x[M][R][-][@][i][m] or
    [-][@]

所以有两种类型：

1. 字符规则形， 如 “LDB-WXVGA”

2. 数字规则形，如"1920*1080"

具体各个参数意义可参照fb_find_mode()函数注释。

3.  kernel cmdline里设置的

本例是：

video=mxcfb0:dev=ldb,LDB-WSVGA,if=RGB24,bpp=32

它会覆盖 tek_fb_data中的值,覆盖规则根据mxcfb后面的值。

比如mxcfb0覆盖tek_fb_data[0], 以此类推。

了解了参数意义之后下面就方便理解了.

系统有如下调用：

static int ldb_disp_init(struct mxc_dispdrv_handle *disp,
    struct mxc_dispdrv_setting *setting) {
......
    ret = fb_find_mode(&setting->fbi->var, setting->fbi, setting->dft_mode_str,
				ldb_modedb, ldb_modedb_sz, NULL, setting->default_bpp);
......
}

本例：

setting->dft_mode_str为： "LDB-WSVGA"

setting->default_bpp为： 32

下面看代码执行流程：

/**
 *    fb_find_mode - finds a valid video mode
 *    @var: frame buffer user defined part of display
 *    @info: frame buffer info structure
 *    @mode_option: string video mode to find
 *    @db: video mode database
 *    @dbsize: size of @db
 *    @default_mode: default video mode to fall back to
 *    @default_bpp: default color depth in bits per pixel
 *
 *    Finds a suitable video mode, starting with the specified mode
 *    in @mode_option with fallback to @default_mode.  If
 *    @default_mode fails, all modes in the video mode database will
 *    be tried.
 *
 *    Valid mode specifiers for @mode_option:
 *
 *    x[M][R][-][@][i][m] or
 *    [-][@]
 *
 *    with , ,  and  decimal numbers and
 *     a string.
 *
 *      If 'M' is present after yres (and before refresh/bpp if present),
 *      the function will compute the timings using VESA(tm) Coordinated
 *      Video Timings (CVT).  If 'R' is present after 'M', will compute with
 *      reduced blanking (for flatpanels).  If 'i' is present, compute
 *      interlaced mode.  If 'm' is present, add margins equal to 1.8%
 *      of xres rounded down to 8 pixels, and 1.8% of yres. The char
 *      'i' and 'm' must be after 'M' and 'R'. Example:
 *
 *      1024x768MR-8@60m - Reduced blank with margins at 60Hz.
 *
 *    NOTE: The passed struct @var is _not_ cleared!  This allows you
 *    to supply values for e.g. the grayscale and accel_flags fields.
 *
 *    Returns zero for failure, 1 if using specified @mode_option,
 *    2 if using specified @mode_option with an ignored refresh rate,
 *    3 if default mode is used, 4 if fall back to any valid mode.
 *
 */
int fb_find_mode(struct fb_var_screeninfo *var,
		 struct fb_info *info, const char *mode_option,
		 const struct fb_videomode *db, unsigned int dbsize,
		 const struct fb_videomode *default_mode,
		 unsigned int default_bpp)
{
    int i;

    /* Set up defaults */
    /*参数未给则使用modedb。*/
    if (!db) {
	db = modedb;
	dbsize = ARRAY_SIZE(modedb);
    }

    /*如果没设置则使用db[0]的值，此例传进来的本身就是db[0]*/
    if (!default_mode)
	default_mode = &db[0];
    /*没有设置bpp则默认使用8bpp，本例是32*/
    if (!default_bpp)
	default_bpp = 8;

    /* Did the user specify a video mode? */
    if (!mode_option)
	mode_option = fb_mode_option;
    /*本例是“LDB-WSVGA”*/
    if (mode_option) {
	const char *name = mode_option;
	unsigned int namelen = strlen(name);
	int res_specified = 0, bpp_specified = 0, refresh_specified = 0;
	unsigned int xres = 0, yres = 0, bpp = default_bpp, refresh = 0;
	int yres_specified = 0, cvt = 0, rb = 0, interlace = 0, margins = 0;
	u32 best, diff, tdiff;
       /*数字格式规则形才会跑下面的循环*/
	for (i = namelen-1; i >= 0; i--) {
	    switch (name[i]) {
                /*@后面的是刷新频率*/
                case '@':
		    namelen = i;
		    if (!refresh_specified && !bpp_specified &&
			!yres_specified) {
			refresh = simple_strtol(&name[i+1], NULL, 10);
			refresh_specified = 1;
			if (cvt || rb)
			    cvt = 0;
		    } else
			goto done;
		    break;
                /*后面是bpp*/
                case '-':
		    namelen = i;
			printk("line:%d\n", __LINE__);
		    if (!bpp_specified && !yres_specified) {
			bpp = simple_strtol(&name[i+1], NULL, 10);
			bpp_specified = 1;
			if (cvt || rb)
			    cvt = 0;
		    } else
			goto done;
		    break;
                /*获取yres*/
		case 'x':
		    if (!yres_specified) {
			yres = simple_strtol(&name[i+1], NULL, 10);
			yres_specified = 1;
		    } else
			goto done;
		    break;
		case '0' ... '9':
		    break;
		case 'M':
		    if (!yres_specified)
			cvt = 1;
		    break;
		case 'R':
		    if (!cvt)
			rb = 1;
		    break;
		case 'm':
		    if (!cvt)
			margins = 1;
		    break;
		case 'i':
		    if (!cvt)
			interlace = 1;
		    break;
		default:
		    goto done;
	    }
	}
        /*如果yres有值，那么也获取xres.*/
        if (i < 0 && yres_specified) {
	    xres = simple_strtol(name, NULL, 10);
	    res_specified = 1;
	}
done:
        /*不会跑这里*/
        if (cvt) {
	    struct fb_videomode cvt_mode;
	    int ret;

	    DPRINTK("CVT mode %dx%d@%dHz%s%s%s\n", xres, yres,
		    (refresh) ? refresh : 60, (rb) ? " reduced blanking" :
		    "", (margins) ? " with margins" : "", (interlace) ?
		    " interlaced" : "");

	    memset(&cvt_mode, 0, sizeof(cvt_mode));
	    cvt_mode.xres = xres;
	    cvt_mode.yres = yres;
	    cvt_mode.refresh = (refresh) ? refresh : 60;

	    if (interlace)
		cvt_mode.vmode |= FB_VMODE_INTERLACED;
	    else
		cvt_mode.vmode &= ~FB_VMODE_INTERLACED;

	    ret = fb_find_mode_cvt(&cvt_mode, margins, rb);

	    if (!ret && !fb_try_mode(var, info, &cvt_mode, bpp)) {
		DPRINTK("modedb CVT: CVT mode ok\n");
		return 1;
	    }

	    DPRINTK("CVT mode invalid, getting mode from database\n");
	}

	DPRINTK("Trying specified video mode%s %ix%i\n",
	    refresh_specified ? "" : " (ignoring refresh rate)", xres, yres);

       /*刷新率没指定*/
       if (!refresh_specified) {
		/*
		 * If the caller has provided a custom mode database and a
		 * valid monspecs structure, we look for the mode with the
		 * highest refresh rate.  Otherwise we play it safe it and
		 * try to find a mode with a refresh rate closest to the
		 * standard 60 Hz.
		 */
		if (db != modedb &&
		    info->monspecs.vfmin && info->monspecs.vfmax &&
		    info->monspecs.hfmin && info->monspecs.hfmax &&
		    info->monspecs.dclkmax) {
			  refresh = 1000;
		} else {
                    /*默认使用60HZ*/
                    refresh = 60;
		}
	}

	diff = -1;
	best = -1;
        /*根据名字以及或者分辨率来匹配。*/
        for (i = 0; i < dbsize; i++) {
		if ((name_matches(db[i], name, namelen) ||
		    (res_specified && res_matches(db[i], xres, yres))) &&
		    !fb_try_mode(var, info, &db[i], bpp)) {
                       /*刷新率也匹配的时候就认准你了！*/
                       if (refresh_specified && db[i].refresh == refresh) {
				return 1;
			} else {
                              /*刷新率不一样就找差得最少的*/  
                              if (abs(db[i].refresh - refresh) < diff) {
					diff = abs(db[i].refresh - refresh);
					best = i;
				}
			}
		}
	}
	/*得到刷新率差得最少的db，然后返回*/
       if (best != -1) {
		fb_try_mode(var, info, &db[best], bpp);
		return (refresh_specified) ? 2 : 1;
	}

	/*跑到这里说明名字和分辨率都不匹配。*/
	diff = 2 * (xres + yres);
	best = -1;
	DPRINTK("Trying best-fit modes\n");
        /*找到分辨率最小的那组数据。*/
        for (i = 0; i < dbsize; i++) {
                DPRINTK("Trying %ix%i\n", db[i].xres, db[i].yres);
		if (!fb_try_mode(var, info, &db[i], bpp)) {
			 tdiff = abs(db[i].xres - xres) +
				abs(db[i].yres - yres);

			 /*
			 * Penalize modes with resolutions smaller
			 * than requested.
			 */
			if (xres > db[i].xres || yres > db[i].yres)
				tdiff += xres + yres;
                       /*差值大的会被保留，说白了，最终就是找到分辨率最小的那组参数。*/
			if (diff > tdiff) {
				diff = tdiff;
				best = i;
			}
		}
	}
       /*获取best对应的var参数。*/
       if (best != -1) {
	    fb_try_mode(var, info, &db[best], bpp);
	    return 5;
	}
    }

    /*运行到这里有两种情况，
     1. 字母规则型(如LDB-WXVGA)，那就是名字不匹配，并且参数检查失败,。
     2. 数字规则性(如1920x1080), 那就是名字不匹配 && 分辨率比ldb_modedb中的小上两倍以上(比如1920x1080 和 320x240)。 */
    DPRINTK("Trying default video mode\n");
    if (!fb_try_mode(var, info, default_mode, default_bpp))
	return 3;

    DPRINTK("Trying all modes\n");
    /*默认的还失败那我只能随便找一个了。*/
    for (i = 0; i < dbsize; i++)
	if (!fb_try_mode(var, info, &db[i], default_bpp))
	    return 4;

    /*随便都不行，那我只能失败了...*/
    DPRINTK("No valid mode found\n");
    return 0;
} 

  其实本例中fb_try_mode返回的都是0，看代码，这里的作用基本上看成是得到当前对应的db值然后放再var中

供后面的framebuffer driver使用。

kernel_imx\drivers\video\modedb.c

static int fb_try_mode(struct fb_var_screeninfo *var, struct fb_info *info,
		       const struct fb_videomode *mode, unsigned int bpp)
{
    int err = 0;

    DPRINTK("Trying mode %s %dx%d-%d@%d\n", mode->name ? mode->name : "noname",
	    mode->xres, mode->yres, bpp, mode->refresh);
    var->xres = mode->xres;
    var->yres = mode->yres;
    var->xres_virtual = mode->xres;
    var->yres_virtual = mode->yres;
    var->xoffset = 0;
    var->yoffset = 0;
    var->bits_per_pixel = bpp;
    var->activate |= FB_ACTIVATE_TEST;
    var->pixclock = mode->pixclock;
    var->left_margin = mode->left_margin;
    var->right_margin = mode->right_margin;
    var->upper_margin = mode->upper_margin;
    var->lower_margin = mode->lower_margin;
    var->hsync_len = mode->hsync_len;
    var->vsync_len = mode->vsync_len;
    var->sync = mode->sync;
    var->vmode = mode->vmode;
    if (info->fbops->fb_check_var)
    	err = info->fbops->fb_check_var(var, info);
    var->activate &= ~FB_ACTIVATE_TEST;
    return err;
}

kernel_imx\drivers\video\mxc\mxc_ipuv3_fb.c

static int mxcfb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
{
	u32 vtotal;
	u32 htotal;
	struct mxcfb_info *mxc_fbi = (struct mxcfb_info *)info->par;


	if (var->xres == 0 || var->yres == 0) {
		return 0;
		}
	/* fg should not bigger than bg */
	if (mxc_fbi->ipu_ch == MEM_FG_SYNC) {
		struct fb_info *fbi_tmp;
		int bg_xres = 0, bg_yres = 0;
		int16_t pos_x, pos_y;

		bg_xres = var->xres;
		bg_yres = var->yres;

		fbi_tmp = found_registered_fb(MEM_BG_SYNC, mxc_fbi->ipu_id);
		if (fbi_tmp) {
			bg_xres = fbi_tmp->var.xres;
			bg_yres = fbi_tmp->var.yres;
		}

		ipu_disp_get_window_pos(mxc_fbi->ipu, mxc_fbi->ipu_ch, &pos_x, &pos_y);

		if ((var->xres + pos_x) > bg_xres)
			var->xres = bg_xres - pos_x;
		if ((var->yres + pos_y) > bg_yres)
			var->yres = bg_yres - pos_y;
	}

	if (var->rotate > IPU_ROTATE_VERT_FLIP)
		var->rotate = IPU_ROTATE_NONE;

	if (var->xres_virtual < var->xres)
		var->xres_virtual = var->xres;

	if (var->yres_virtual < var->yres)
		var->yres_virtual = var->yres * 3;

	if ((var->bits_per_pixel != 32) && (var->bits_per_pixel != 24) &&
	    (var->bits_per_pixel != 16) && (var->bits_per_pixel != 12) &&
	    (var->bits_per_pixel != 8))
		var->bits_per_pixel = 16;

	if (check_var_pixfmt(var))
		/* Fall back to default */
		bpp_to_var(var->bits_per_pixel, var);

	if (var->pixclock < 1000) {
		htotal = var->xres + var->right_margin + var->hsync_len +
		    var->left_margin;
		vtotal = var->yres + var->lower_margin + var->vsync_len +
		    var->upper_margin;
		var->pixclock = (vtotal * htotal * 6UL) / 100UL;
		var->pixclock = KHZ2PICOS(var->pixclock);
		dev_dbg(info->device,
			"pixclock set for 60Hz refresh = %u ps\n",
			var->pixclock);
	}

	if (var->height == 0 && mxc_fbi->panel_height_mm)
		var->height = mxc_fbi->panel_height_mm;
	else if (var->height == 0)
		var->height = -1;

	if (var->width == 0 && mxc_fbi->panel_width_mm)
		var->width = mxc_fbi->panel_width_mm;
	else if (var->width == 0)
		var->width = -1;

	var->grayscale = 0;

	return 0;
}