fb: auto-configure with EDID

Use EDID when available to configure the frame buffer driver with
good settings for the attached display.

Change-Id: I69a78155a93e55ffa1ca3ff6621a879a56cdbceb

drivers/fb/Makefile

@@ -3,7 +3,14 @@ PROG=	fb
 
 .include "arch/${MACHINE_ARCH}/Makefile.inc"
 
-SRCS+=	fb.c
+SRCS+=	fb_edid.c fb.c
+
+# re-use EDID parsing/validation code from NetBSD.
+.PATH: ${NETBSDSRCDIR}/sys/dev/videomode
+SRCS+=	edid.c pickmode.c videomode.c vesagtf.c
+
+# Put this dir and the EDID headers (dev/videomode/*.h) in the search path.
+CPPFLAGS+= -I${.CURDIR} -I${NETBSDSRCDIR}/sys
 
 DPADD+=	${LIBCHARDRIVER} ${LIBSYS}
 LDADD+=	-lchardriver -lsys

drivers/fb/README.txt

@@ -0,0 +1,24 @@
+Frame Buffer Driver
+===================
+
+Overview
+--------
+
+This is the driver for the frame buffer. Currently it only supports the
+DM37XX (BeagleBoard-xM).
+
+Testing the Code
+----------------
+
+Starting up an instance:
+
+service up /usr/sbin/fb -dev /dev/fb0 -args edid.0=cat24c256.3.50
+
+The arguments take the following form:
+
+	edid.X=L where X is the frame buffer device (usually 0) and L is
+	the service label of the service to perform the EDID reading. In
+	the example above, it's the EEPROM with slave address 0x50 on
+	the 3rd I2C bus. If you want to use the defaults and skip EDID
+	reading, you may omit the arguments.
+

drivers/fb/arch/earm/fb_arch.c

@@ -1,23 +1,50 @@
-/* Architecture dependent part for the framebuffer on the OMAP3. Since we don't
+/* Architecture dependent part for the framebuffer on the OMAP3.
- * have support for EDID (which requires support for i2c, also something we
+ * There's obvious room for improvement.
- * don't have, yet), but we do have a screen with 1024*600 resolution for our
+ */
- * testing purposes, we hardcode that resolution here. There's obvious room for
- * improvement. */
 
 #include <minix/chardriver.h>
 #include <minix/drivers.h>
 #include <minix/fb.h>
 #include <minix/type.h>
 #include <minix/vm.h>
+#include <minix/log.h>
 #include <assert.h>
 #include <sys/mman.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h>
+#include <dev/videomode/videomode.h>
+#include <dev/videomode/edidvar.h>
+#include <dev/videomode/edidreg.h>
 #include "dss.h"
+#include "fb.h"
+
+/* default / fallback resolution if EDID reading fails */
 #define SCREEN_WIDTH 1024
 #define SCREEN_HEIGHT 600
 #define PAGES_NR 2
 
+#define NSUPPORTED_MODES (4)
+
+/* List of valid modes from TRM 7.1
+ * Other modes might work (like the default 1024x600), but no guarantees.
+ */
+struct supported_modes {
+	int hdisplay;
+	int vdisplay;
+} omap_supported_modes[NSUPPORTED_MODES] = {
+	{ .hdisplay = 1024, .vdisplay = 768 }, /* XGA */
+	{ .hdisplay = 1280, .vdisplay = 800 }, /* WXGA */
+	{ .hdisplay = 1400, .vdisplay = 1050 }, /* SXGA+ */
+	{ .hdisplay = 1280, .vdisplay = 720 } /* HD 720p */
+};
+
+/* local function prototypes */
+static struct videomode *choose_mode(struct edid_info *info);
+static void configure_with_defaults(int minor);
+static int configure_with_edid(int minor, struct edid_info *info);
+
+/* globals */
 static vir_bytes dss_phys_base;		/* Address of dss phys memory map */
 static vir_bytes dispc_phys_base;	/* Address of dispc phys memory map */
 static vir_bytes fb_vir;
@@ -50,7 +77,9 @@ static const struct panel_config default_cfg = {
         .panel_color    = 0xFFFFFF	/* WHITE */
 };
 
-static const struct fb_fix_screeninfo fbfs = {
+static struct panel_config omap_cfg[FB_DEV_NR];
+
+static const struct fb_fix_screeninfo default_fbfs = {
 	.xpanstep	= 0,
 	.ypanstep	= 0,
 	.ywrapstep	= 0,
@@ -59,7 +88,9 @@ static const struct fb_fix_screeninfo fbfs = {
 	.mmio_len	= 0	/* these are set to 0 */
 };
 
-static struct fb_var_screeninfo fbvs = {
+static struct fb_fix_screeninfo omap_fbfs[FB_DEV_NR];
+
+static const struct fb_var_screeninfo default_fbvs = {
 	.xres		= SCREEN_WIDTH,
 	.yres		= SCREEN_HEIGHT,
 	.xres_virtual	= SCREEN_WIDTH,
@@ -89,6 +120,15 @@ static struct fb_var_screeninfo fbvs = {
 		}
 };
 
+static struct fb_var_screeninfo omap_fbvs[FB_DEV_NR];
+
+/* logging - use with log_warn(), log_info(), log_debug(), log_trace() */
+static struct log log = {
+	.name = "fb",
+	.log_level = LEVEL_INFO,
+	.log_func = default_log
+};
+
 static inline u32_t
 readw(vir_bytes addr)
 {
@@ -101,6 +141,97 @@ writew(vir_bytes addr, u32_t val)
         *((volatile u32_t *) addr) = val;
 }
 
+static struct videomode *
+choose_mode(struct edid_info *info)
+{
+	int i, j;
+
+	/* choose the highest resolution supported by both the SoC and screen */
+	for (i = info->edid_nmodes - 1; i >= 0; i--) {
+		for (j = NSUPPORTED_MODES - 1; j >= 0; j--) {
+
+			if (info->edid_modes[i].hdisplay ==
+				omap_supported_modes[j].hdisplay &&
+				info->edid_modes[i].vdisplay ==
+				omap_supported_modes[j].vdisplay) {
+
+				return &(info->edid_modes[i]);
+			}
+		}
+	}
+
+	return NULL;
+}
+
+static int
+configure_with_edid(int minor, struct edid_info *info)
+{
+	struct videomode *mode;
+
+	if (info == NULL || minor < 0 || minor >= FB_DEV_NR) {
+		log_warn(&log, "Invalid minor #%d or info == NULL\n", minor);
+		return -1;
+	}
+
+	/* If debugging or tracing, print the contents of info */
+	if (log.log_level >= LEVEL_DEBUG) {
+		log_debug(&log, "--- EDID - START ---\n");
+		edid_print(info);
+		log_debug(&log, "--- EDID - END ---\n");
+	}
+
+	/* Choose the preferred mode. */
+	mode = choose_mode(info);
+	if (mode == NULL) {
+		log_warn(&log, "Couldn't find a supported resolution.\n");
+		return -1;
+	}
+
+	/*
+	 * apply the default settings since we don't overwrite every field
+	 */
+	configure_with_defaults(minor);
+
+	/*
+	 * apply the settings corresponding to the given EDID
+	 */
+
+	/* panel_config */
+	omap_cfg[minor].lcd_size    = ((mode->vdisplay - 1) << 16 | (mode->hdisplay - 1));
+
+	if (EDID_FEATURES_DISP_TYPE(info->edid_features) ==
+			EDID_FEATURES_DISP_TYPE_MONO) {
+		omap_cfg[minor].panel_type  = 0x00;		/* Mono */
+	} else {
+		omap_cfg[minor].panel_type  = 0x01;		/* RGB/Color */
+	}
+
+	/* fb_fix_screeninfo */
+	omap_fbfs[minor].line_length = mode->hdisplay * 4;
+
+	/* fb_var_screeninfo */
+	omap_fbvs[minor].xres		= mode->hdisplay;
+	omap_fbvs[minor].yres		= mode->vdisplay;
+	omap_fbvs[minor].xres_virtual	= mode->hdisplay;
+	omap_fbvs[minor].yres_virtual	= mode->vdisplay*2;
+
+	return OK;
+}
+
+static void
+configure_with_defaults(int minor)
+{
+	if (minor < 0 || minor >= FB_DEV_NR) {
+		log_warn(&log, "Invalid minor #%d\n", minor);
+		return;
+	}
+
+	/* copy the default values into this minor's configuration */
+	memcpy(&omap_cfg[minor], &default_cfg, sizeof(struct panel_config));
+	memcpy(&omap_fbfs[minor], &default_fbfs, sizeof(struct fb_fix_screeninfo));
+	memcpy(&omap_fbvs[minor], &default_fbvs, sizeof(struct fb_var_screeninfo));
+}
+
 static void
 arch_configure_display(int minor)
 {
@@ -110,7 +241,7 @@ arch_configure_display(int minor)
 	if (!initialized) return;
 	if (minor != 0) return;
 
-	off = fbvs.yoffset * fbvs.xres_virtual * (fbvs.bits_per_pixel/8);
+	off = omap_fbvs[minor].yoffset * omap_fbvs[minor].xres_virtual * (omap_fbvs[minor].bits_per_pixel/8);
 
 	writew((vir_bytes) OMAP3_DISPC_GFX_BA0(dispc_phys_base),
 		fb_phys + (phys_bytes) off);
@@ -136,7 +267,7 @@ arch_get_varscreeninfo(int minor, struct fb_var_screeninfo *fbvsp)
 	if (!initialized) return ENXIO;
 	if (minor != 0) return ENXIO;
 
-	*fbvsp = fbvs;
+	*fbvsp = omap_fbvs[minor];
 	return OK;
 }
 
@@ -151,12 +282,12 @@ arch_put_varscreeninfo(int minor, struct fb_var_screeninfo *fbvsp)
 	if (minor != 0)	return ENXIO;
 
 	/* For now we only allow to play with the yoffset setting */
-	if (fbvsp->yoffset != fbvs.yoffset) {
+	if (fbvsp->yoffset != omap_fbvs[minor].yoffset) {
-		if (fbvsp->yoffset < 0 || fbvsp->yoffset > fbvs.yres) {
+		if (fbvsp->yoffset < 0 || fbvsp->yoffset > omap_fbvs[minor].yres) {
 			return EINVAL;
 		}
 
-		fbvs.yoffset = fbvsp->yoffset;
+		omap_fbvs[minor].yoffset = fbvsp->yoffset;
 	}
 	
 	/* Now update hardware with new settings */
@@ -170,7 +301,7 @@ arch_get_fixscreeninfo(int minor, struct fb_fix_screeninfo *fbfsp)
 	if (!initialized) return ENXIO;
 	if (minor != 0) return ENXIO;
 
-	*fbfsp = fbfs;
+	*fbfsp = omap_fbfs[minor];
 	return OK;
 }
 
@@ -181,20 +312,32 @@ arch_pan_display(int minor, struct fb_var_screeninfo *fbvsp)
 }
 
 int
-arch_fb_init(int minor, struct device *dev)
+arch_fb_init(int minor, struct device *dev, struct edid_info *info)
 {
+	int r;
 	u32_t rdispc;
 	struct minix_mem_range mr;
 
-	const struct panel_config *panel_cfg = &default_cfg;
+	const struct panel_config *panel_cfg = &omap_cfg[minor];
 
 	assert(dev != NULL);
 	if (minor != 0) return ENXIO;	/* We support only one minor */
 
+
 	if (initialized) {
 		dev->dv_base = fb_vir;
 		dev->dv_size = fb_size;
 		return OK;
+	} else if (info != NULL) {
+		log_debug(&log, "Configuring Settings based on EDID...\n");
+		r = configure_with_edid(minor, info);
+		if (r != OK) {
+			log_warn(&log, "EDID config failed. Using defaults.\n");
+			configure_with_defaults(minor);
+		}
+	} else {
+		log_debug(&log, "Loading Default Settings...\n");
+		configure_with_defaults(minor);
 	}
 
 	initialized = 1;
@@ -254,8 +397,8 @@ arch_fb_init(int minor, struct device *dev)
 	writew(OMAP3_DISPC_GFX_PIXEL_INC(dispc_phys_base), 1);
 
 	/* Allocate contiguous physical memory for the display buffer */
-	fb_size = fbvs.yres_virtual * fbvs.xres_virtual *
+	fb_size = omap_fbvs[minor].yres_virtual * omap_fbvs[minor].xres_virtual *
-				(fbvs.bits_per_pixel / 8);
+				(omap_fbvs[minor].bits_per_pixel / 8);
 	fb_vir = (vir_bytes) alloc_contig(fb_size, 0, &fb_phys);
 	if (fb_vir == (vir_bytes) MAP_FAILED) {
 		panic("Unable to allocate contiguous memory\n");

drivers/fb/fb.c

@@ -11,10 +11,15 @@
 #include <sys/mman.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h>
+#include <dev/videomode/videomode.h>
+#include <dev/videomode/edidvar.h>
+#include <dev/videomode/edidreg.h>
+
 #include "logos.h"
+#include "fb_edid.h"
 #include "fb.h"
 
-#define FB_DEV_NR	1
 /*
  * Function prototypes for the fb driver.
  */
@@ -69,11 +74,19 @@ static int open_counter[FB_DEV_NR];		/* Open count */
 static int
 fb_open(message *m)
 {
+	int r;
 	static int initialized = 0;
+	static struct edid_info info;
+	static struct edid_info *infop = NULL;
 
 	if (m->DEVICE < 0 || m->DEVICE >= FB_DEV_NR) return ENXIO;
 
-	if (arch_fb_init(m->DEVICE, &fb_device[m->DEVICE]) == OK) {
+	if (!initialized) {
+		r = fb_edid_read(m->DEVICE, &info);
+		infop = (r == 0) ? &info : NULL;
+	}
+
+	if (arch_fb_init(m->DEVICE, &fb_device[m->DEVICE], infop) == OK) {
 		open_counter[m->DEVICE]++;
 		if (!initialized) {
 			if (has_restarted) {
@@ -363,8 +376,11 @@ sef_cb_init(int type, sef_init_info_t *UNUSED(info))
 }
 
 int
-main(void)
+main(int argc, char *argv[])
 {
+	env_setargs(argc, argv);
+	fb_edid_args_parse();
+
 	sef_local_startup();
 	chardriver_task(&fb_tab, CHARDRIVER_SYNC);
 	return OK;

drivers/fb/fb.h

@@ -1,7 +1,9 @@
 #ifndef __FB_H__
 #define __FB_H__
 
-int arch_fb_init(int minor, struct device *dev);
+#include <minix/fb.h>
+
+int arch_fb_init(int minor, struct device *dev, struct edid_info *info);
 int arch_get_device(int minor, struct device *dev);
 int arch_get_varscreeninfo(int minor, struct fb_var_screeninfo *fbvsp);
 int arch_put_varscreeninfo(int minor, struct fb_var_screeninfo *fbvs_copy);
@@ -9,5 +11,6 @@ int arch_get_fixscreeninfo(int minor, struct fb_fix_screeninfo *fbfsp);
 int arch_pan_display(int minor, struct fb_var_screeninfo *fbvs_copy);
 
 #define FB_MESSAGE "Hello, world! From framebuffer!\n"
+#define FB_DEV_NR 1
 
 #endif /* __FB_H__ */

drivers/fb/fb_edid.c

@@ -0,0 +1,188 @@
+/*
+ * Handle reading the EDID information, validating it, and parsing it into
+ * a struct edid_info. EDID reads are done using the Block Device Protocol
+ * as it's already supported by the cat24c256 driver and there is no need
+ * to add yet another message format/type.
+ */
+
+#include <minix/fb.h>
+#include <minix/chardriver.h>
+#include <minix/drivers.h>
+#include <minix/ds.h>
+#include <minix/rs.h>
+#include <minix/log.h>
+#include <minix/sysutil.h>
+#include <minix/type.h>
+#include <minix/vm.h>
+#include <sys/ioc_fb.h>
+#include <assert.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <dev/videomode/videomode.h>
+#include <dev/videomode/edidvar.h>
+#include <dev/videomode/edidreg.h>
+
+#include "fb_edid.h"
+#include "fb.h"
+
+static int do_read(endpoint_t endpt, uint8_t *buf, size_t bufsize);
+
+/* logging - use with log_warn(), log_info(), log_debug(), log_trace() */
+static struct log log = {
+	.name = "edid",
+	.log_level = LEVEL_INFO,
+	.log_func = default_log
+};
+
+/*
+ * Labels corresponding to drivers which provide EDID.
+ */
+static char edid_providers[FB_DEV_NR][RS_MAX_LABEL_LEN+1];
+
+/*
+ * Populate edid_providers from command line arguments. The service command
+ * should get EDID providers like this: "-args edid.0=tda19988.1.3470" where
+ * 0 is the minor number of the frame buffer, tda19988 is the device driver,
+ * 1 is the i2c bus and 3470 is the slave address (the TDA19988 has 2 slave
+ * addresses 0x34 and 0x70).
+ */
+int
+fb_edid_args_parse(void)
+{
+	int i;
+	int r;
+	char key[32];
+
+	for (i = 0; i < FB_DEV_NR; i++) {
+
+		memset(key, '\0', 32);
+		snprintf(key, 32, "edid.%d", i);
+
+		memset(edid_providers[i], '\0', RS_MAX_LABEL_LEN);
+		r = env_get_param(key, edid_providers[i], RS_MAX_LABEL_LEN);
+		if (r == OK) {
+			log_debug(&log, "Found key:%s value:%s\n", key, edid_providers[i]);
+		} else {
+			/* not an error, user is allowed to omit EDID
+			 * providers in order to skip EDID reading and use
+			 * the default settings.
+			 */
+			log_debug(&log, "Couldn't find key:%s\n", key);
+		}
+	}
+
+	return OK;
+}
+
+/*
+ * Send a read request to the block driver at endpoint endpt.
+ */
+static int
+do_read(endpoint_t driver_endpt, uint8_t *buf, size_t bufsize)
+{
+	int r;
+	message m;
+	cp_grant_id_t grant_nr;
+
+	/* Open Device - required for drivers using libblockdriver */
+	memset(&m, '\0', sizeof(message));
+	m.m_type = BDEV_OPEN;
+	m.BDEV_ACCESS = R_BIT;
+	m.BDEV_ID = 0;
+	m.BDEV_MINOR = 0;
+
+	r = sendrec(driver_endpt, &m);
+	if (r != OK) {
+		log_debug(&log, "sendrec(BDEV_OPEN) failed (r=%d)\n", r);
+		return r;
+	}
+
+	grant_nr = cpf_grant_direct(driver_endpt, (vir_bytes) buf,
+		bufsize, CPF_READ | CPF_WRITE);
+
+	/* Perform the read */
+	memset(&m, '\0', sizeof(message));
+	m.m_type = BDEV_READ;
+	m.BDEV_MINOR = 0;
+	m.BDEV_COUNT = bufsize;
+	m.BDEV_GRANT = grant_nr;
+	m.BDEV_FLAGS = BDEV_NOPAGE; /* the EEPROMs used for EDID are pageless */
+	m.BDEV_ID = 0;
+	m.BDEV_POS_LO = 0;
+	m.BDEV_POS_HI = 0;
+
+	r = sendrec(driver_endpt, &m);
+	cpf_revoke(grant_nr);
+	if (r != OK) {
+		log_debug(&log, "sendrec(BDEV_READ) failed (r=%d)\n", r);
+		/* Clean-up: try to close the device */
+		memset(&m, '\0', sizeof(message));
+		m.m_type = BDEV_CLOSE;
+		m.BDEV_MINOR = 0;
+		m.BDEV_ID = 0;
+		sendrec(driver_endpt, &m);
+		return r;
+	}
+
+	/* Close the device */
+	memset(&m, '\0', sizeof(message));
+	m.m_type = BDEV_CLOSE;
+	m.BDEV_MINOR = 0;
+	m.BDEV_ID = 0;
+	r = sendrec(driver_endpt, &m);
+	if (r != OK) {
+		log_debug(&log, "sendrec(BDEV_CLOSE) failed (r=%d)\n", r);
+		return r;
+	}
+
+	return bufsize;
+}
+
+int
+fb_edid_read(int minor, struct edid_info *info)
+{
+
+	int r;
+	uint8_t buffer[128];
+	endpoint_t endpt;
+
+	if (info == NULL || minor < 0 || minor >= FB_DEV_NR ||
+					edid_providers[minor][0] == '\0') {
+		return EINVAL;
+	}
+
+	log_debug(&log, "Contacting %s to get EDID.\n", edid_providers[minor]);
+
+	/* Look up the endpoint that corresponds to the label */
+	endpt = 0;
+	r = ds_retrieve_label_endpt(edid_providers[minor], &endpt);
+	if (r != 0 || endpt == 0) {
+		log_warn(&log, "Couldn't find endpoint for label '%s'\n", edid_providers[minor]);
+		return r;
+	}
+
+	/* Perform the request and put the resulting EDID into the buffer. */
+	memset(buffer, 0x00, 128);
+	r = do_read(endpt, buffer, 128);
+	if (r < 0) {
+		log_debug(&log, "Failed to read EDID\n");
+		return r;
+	}
+
+	/* parse and validate EDID */
+	r = edid_parse(buffer, info);
+	if (r != 0) {
+		log_warn(&log, "Invalid EDID data in buffer.\n");
+		return r;
+	} 
+
+	log_debug(&log, "EDID Retrieved and Parsed OK\n");
+
+	return OK;
+}
+

drivers/fb/fb_edid.h

@@ -0,0 +1,12 @@
+#ifndef __EDID_H
+#define __EDID_H
+
+#include <stdint.h>                                                             
+#include <dev/videomode/videomode.h>                                            
+#include <dev/videomode/edidvar.h>                                              
+#include <dev/videomode/edidreg.h>
+
+int fb_edid_args_parse(void);
+int fb_edid_read(int minor, struct edid_info *info);
+
+#endif /* __EDID_H */

etc/system.conf

@@ -573,7 +573,7 @@ service fb
 		PRIVCTL		#  4
         ;
 	ipc
-                SYSTEM pm rs ds vm vfs tda19988
+                SYSTEM pm rs ds vm vfs cat24c256 tda19988
 	;
 };
 

etc/usr/rc

@@ -197,10 +197,14 @@ start)
 
 	BOARD_NAME=`eepromread -i | sed -n 's/^BOARD_NAME      : \(.*\)$/\1/p'`
 	case "${BOARD_NAME}" in
+
 		A335BONE)
 			echo "Detected BeagleBone"
 			echo -n "Starting i2c device drivers: "
-			test -e /dev/eepromb1s50 || (cd /dev && MAKEDEV eepromb1s50)
+
+			# start EEPROM driver for reading board info
+			test -e /dev/eepromb1s50 || \
+				(cd /dev && MAKEDEV eepromb1s50)
 			up cat24c256 -dev /dev/eepromb1s50 \
 				-label cat24c256.1.50 \
 				-args 'bus=1 address=0x50'
@@ -209,13 +213,35 @@ start)
 			up tps65217 -label tps65217.1.24 \
 			        -args 'bus=1 address=0x24'
 
+			# check for the presence of a display
+			eepromread -f /dev/i2c-2 -n > /dev/null 2>&1
+			RESULT=$?
+			if [ $RESULT -eq 0 ]
+			then
+				# start eeprom driver for reading EDID.
+				test -e /dev/eepromb2s50 || \
+					(cd /dev && MAKEDEV eepromb2s50)
+				up cat24c256 -dev /dev/eepromb2s50 \
+					-label cat24c256.2.50 \
+					-args 'bus=2 address=0x50'
+
+				# start frame buffer
+				#up fb -dev /dev/fb0 -args edid.0=cat24c256.2.50
+				# fb hasn't been ported to AM335X yet.
+			fi
+
 			;;
+
 		A335BNLT)
 			echo "Detected BeagleBone Black"
 			echo -n "Starting i2c device drivers: "
-			test -e /dev/eepromb1s50 || (cd /dev && MAKEDEV eepromb1s50)
+
+			# start EEPROM driver for reading board info
+			test -e /dev/eepromb1s50 || \
+				(cd /dev && MAKEDEV eepromb1s50)
 			up cat24c256 -dev /dev/eepromb1s50 \
-				-label cat24c256.1.50 -args 'bus=1 address=0x50'
+				-label cat24c256.1.50 \
+				-args 'bus=1 address=0x50'
 
 			# Start TPS65217 driver for power management.
 			up tps65217 -label tps65217.1.24 \
@@ -224,7 +250,13 @@ start)
 			# Start TDA19988 driver for reading EDID.
 			up tda19988 -label tda19988.1.3470 -args \
 				'cec_bus=1 cec_address=0x34 hdmi_bus=1 hdmi_address=0x70'
+
+			# start frame buffer
+			#up fb -dev /dev/fb0 -args edid.0=tda19988.1.3470
+			# fb hasn't been ported to AM335X yet.
+
 			;;
+
 		UNKNOWN)
 			echo "Unable to detect board -- assuming BeagleBoard-xM"
 			echo -n "Starting i2c device drivers: "
@@ -236,6 +268,22 @@ start)
 			# Set the system time to the time in the TPS65950's RTC
 			readclock
 
+			# check for the presence of a display
+			eepromread -f /dev/i2c-3 -n > /dev/null 2>&1
+			RESULT=$?
+			if [ $RESULT -eq 0 ]
+			then
+				# start eeprom driver for reading edid
+				test -e /dev/eepromb3s50 || \
+					(cd /dev && MAKEDEV eepromb3s50)
+				up cat24c256 -dev /dev/eepromb3s50 \
+					-label cat24c256.3.50 \
+					-args 'bus=3 address=0x50'
+
+				# start frame buffer
+				up fb -dev /dev/fb0 -args edid.0=cat24c256.3.50
+			fi
+
 			;;
 	esac