Enabling 16 bit LCD mode for Beaglebone Black

Hi Ulf,

Please check AM335X Errata Usage Note 3.1.1. You will notice that red and blue color output pins are swapped for 16 and 24 bit mode. If you set the LCD controller in 16-bit mode you will not be able to use the HDMI output. I will ask a software expert to check what you need to change in the device tree for 16-bit mode.

OK, studied what happen a little bit more.

The Graphics driver used is the omaplfb. This comes from the omap3-sgx-modules recipe.

I guess, I need to have the DeviceTree setup for the Graphic Toolkit

(Graphics_SDK_setuplinux_hardfp_5_01_01_01.bin)

Hi Ulf,

You need to remove the upper 8 signal bits from the device tree lcd pinmux configuration:

                0x20 0x01    /* gpmc_ad8.lcd_data16, OUTPUT | MODE1 */
                0x24 0x01    /* gpmc_ad9.lcd_data17, OUTPUT | MODE1 */
                0x28 0x01    /* gpmc_ad10.lcd_data18, OUTPUT | MODE1 */
                0x2c 0x01    /* gpmc_ad11.lcd_data19, OUTPUT | MODE1 */
                0x30 0x01    /* gpmc_ad12.lcd_data20, OUTPUT | MODE1 */
                0x34 0x01    /* gpmc_ad13.lcd_data21, OUTPUT | MODE1 */
                0x38 0x01    /* gpmc_ad14.lcd_data22, OUTPUT | MODE1 */
                0x3c 0x01    /* gpmc_ad15.lcd_data23, OUTPUT | MODE1 */

You also need to change the .bpp member of the panel-info structure to 16.

Best regards,
Miroslav

The Framebuffer driver is

root@beaglebone:/proc# cat fb
0 DA8xx FB Drv

code in drivers/video/da8xx-fb.c

Device Tree for this is documented in <kernel>/Documentation/devicetree/bindings/video/da8xx-fb.txt

which does not mention bits per pixel.

Can you configure the bits per pixel in this driver using device-tree?

I can see, that you can do this in platform data, but cannot find any definition of any platform data.

Could You check my device file?

I tried shortcircuiting the device-tree file, and hardwired the driver to 16 bits per pixel

bpp = 16;

But that did not work at all with the LCD4.

Then I tried swapping colours.

static int fb_check_var(struct fb_var_screeninfo *var,
            struct fb_info *info)
{

...
    switch (var->bits_per_pixel) {

...

    case 32:
        var->transp.offset = 24;
        var->transp.length = 8;
#ifdef CONFIG_FB_DA8XX_RGB

       /* New configuration */

        var->red.offset = 0;
        var->red.length = 8;
        var->green.offset = 8;
        var->green.length = 8;
        var->blue.offset = 16;
        var->blue.length = 8;
        var->nonstd = 0;
#else

        /* Original */
        var->red.offset = 16;
        var->red.length = 8;
        var->green.offset = 8;
        var->green.length = 8;
        var->blue.offset = 0;
        var->blue.length = 8;
        var->nonstd = 0;
#endif
        break;
    default:
        err = -EINVAL;
    }

...

}

And then omaplfb fails to initialize.

[   37.214978] omaplfb: OMAPLFBInitFBDev: Device 0: Unknown FB format

I can get things running, by setting the framebuffer to 16 bits, before psplash runs.

/etc/rcS.d/S00fbdepth

-----------------------------------

#!/bin/sh

fbset -depth 16

-----------------------------------

This is ugly, though (and Tux has Blue feet)

I do not think it will work, setting bpp = 16 in the panel-info structure.

The panel-info is handled by the tilcdc-panel.c file, which does not even get compiled

when you are using the da8xx-fb driver. Only when you are using the tilcdc driver.

So the question remains: How do you set 16 bit mode for the da8xx-fb driver in a device-tree file?

Hi Ulf,

Did you ever get this figured out?  

I've got the same problem with a custom 5.7' display on a BBB.  I added the panel info into my custom dts file and it had no effect, reading this thread, now I know why.

Regards,

Greg

Hi Ulf,
Hi all,

I am using Android JB 4.2.2(kernel version is 3.2) for custom 7' BBB. I have to configure the panel in RGB565 mode as explained in Figure 3 of the ti errata sheet(3.1.1 LCD: Color Assignments of LCD_DATA Terminals). As per I know we have to set the bpp to 16 in a board file. But I am not getting the expected result. On the board I am getting the "LCDC sync lost" message. Please let me know if anyone is faced the similar issue and let me know is there any other code changes we have to do to support the RGB565 mode.

Here is some progress I made in my cutom board. But I struck at issue explained in the link.https://e2e.ti.com/support/arm/sitara_arm/f/791/p/264290/1582201#1582201