// written by Boris Posavec (akiko/agt), 2012.
// this is just a snippet, not compilable without some other files from the project.
// demonstrates how to open, mmap, and communicate with /dev/fbN devices
// on OMAP.

#include "sys/omapfb.h"

int fb0_fd = 0;
int fb1_fd = 0;
#define TS_DEV0 "/dev/fb0"
#define TS_DEV1 "/dev/fb1"

struct fb_fix_screeninfo fixinfo;
struct fb_var_screeninfo varinfo;
struct omapfb_mem_info meminfo;
struct omapfb_plane_info planeinfo;

enum fbdev_t
{
	FBDEV_0,
	FBDEV_1,
};

int __read_varinfo(fbdev_t dev)
{
	int fb = (dev == FBDEV_0 ? fb0_fd : fb1_fd);
	if (ioctl(fb, FBIOGET_VSCREENINFO, &varinfo) == -1)
	{
		LOG("error: %s\n", strerror(errno));
		return -1;
	}
	return 0;
}

int __write_varinfo(fbdev_t dev)
{
	int fb = (dev == FBDEV_0 ? fb0_fd : fb1_fd);
	if (ioctl(fb, FBIOPUT_VSCREENINFO, &varinfo) == -1)
	{
		LOG("error: %s\n", strerror(errno));
		return -1;
	}
	return 0;
}

bool fb_init()
{
	int res;
	fb0_fd = open(TS_DEV, O_RDWR);
	if (fb0_fd == -1)
	{
		LOG("Error: cannot open %s \n", TS_DEV);
		return false;
	}

	res = ioctl(fb0_fd, OMAPFB_QUERY_MEM, &meminfo);
	if (res != 0)
	{
		LOG("Error: cannot query omap mem for %s, %d\n", TS_DEV, res);
		return false;
	}
	LOG("fb memsize: %d\n", meminfo.size);

	// mmap it
	fb0 = (unsigned char*) mmap(NULL, meminfo.size, PROT_WRITE, MAP_SHARED, fb0_fd, 0);
	if (fb0 == MAP_FAILED)
	{
		LOG("Error: cannot map %s\n", TS_DEV0);
		return false;
	}
	LOG("%s mapped OK.\n", TS_DEV1);

	// Setup overlay.
	fb1_fd = open(TS_DEV1, O_RDWR);
	if (fb1_fd == -1)
	{
		LOG("Error: cannot open %s \n", TS_DEV1);
		return false;
	}

	res = ioctl(fb1_fd, OMAPFB_QUERY_MEM, &meminfo);
	if (res != 0)
	{
		LOG("Error: cannot query omap mem for %s, %d\n", TS_DEV1, res);
		return false;
	}
	LOG("fb memsize: %d\n", meminfo.size);

	// mmap it
	fb1 = (unsigned char*) mmap(NULL, meminfo.size, PROT_WRITE, MAP_SHARED, fb1_fd, 0);
	if (fb1 == MAP_FAILED)
	{
		LOG("Error: cannot map %s\n", TS_DEV1);
		return false;
	}
	LOG("%s mapped OK.\n", TS_DEV1);

	// Enable overlay
	ioctl(fb1_fd, OMAPFB_QUERY_PLANE, &planeinfo);
	fprintf(stderr, "x, y, w, h, chnout, enabled: %d %d %d %d %d %d\n", planeinfo.pos_x, planeinfo.pos_y, planeinfo.out_width, planeinfo.out_height, planeinfo.channel_out, planeinfo.enabled);
	planeinfo.enabled = 1;
	ioctl(fb1_fd, OMAPFB_SETUP_PLANE, &planeinfo);

	// Enable overlaying, set white as chroma key color
	execute_shell_cmd("echo \"1\" > /sys/devices/platform/omapdss/manager0/alpha_blending_enabled");
	execute_shell_cmd("echo \"1\" > /sys/devices/platform/omapdss/manager0/trans_key_enabled");
	execute_shell_cmd("echo \"0xf81f\" > /sys/devices/platform/omapdss/manager0/trans_key_value");

	// Rotate 180deg
	execute_shell_cmd("echo \"1\" >  /sys/class/graphics/fb0/rotate"); // gui/input
	execute_shell_cmd("echo \"3\" >  /sys/class/graphics/fb1/rotate"); // camera

	// get current xres, yres
	__read_varinfo(FBDEV_0);
	xres = varinfo.xres;
	yres = varinfo.yres;
	bpp = varinfo.bits_per_pixel;

	return true;
}

dev.modmancer.com

demonstrates how to open, mmap, and communicate with /dev/fbN devices on OMAP. won't compile such as, but it's enough to give an insight in how-to.

/dev/fb poking on OMAP

C