AM4378: U-Boot Splash Screen

how do I know what values to use for the panel_config structure that HYEONJAE CHOI uses in omap3_dss.c?

You should tune these values according the display's TRM.

Okay but how do the values in the datasheet correspond to the hex values? The display that he is using is 1280x800. How does that translate to 0x031f04ff? Or how does 24 bit RGB correspond to 0x3?

I think I figured out what to use timing values.

But it seems like in board.c, HYEONJAE CHOI is still using GPIOs to try to turn on the backlight, correct? I don't have any GPIOs controlling the backlight so how do I turn it on during U-Boot?

Hello Tanner,

To turn on the backlight in U-Boot, define

#define GPIO_BACKLIGHT_EN       GPIO_TO_PIN(0, 7)

and use this function to enable and disable the backlight.

void lcdbacklight(int on)
{
        gpio_request(GPIO_BACKLIGHT_EN, "backlight_en");
        if (on)
                gpio_direction_output(GPIO_BACKLIGHT_EN, 0);
        else
                gpio_direction_output(GPIO_BACKLIGHT_EN, 1);
}

Best regards,
Kemal

Where are GPIO_TO_PIN() and gpio_request() defined? I'm getting compiler errors when I try to build

Okay. In the functions lcd_backlight_1() and enable_lcd_power(), there are a few GPIOs that are enabled and set as outputs. What are these GPIOs? How do I know which ones to use for my board?

Remove the lcd_backlight_1(), you already have it implemented by void lcdbacklight(int on) function. enable_lcd_power() drives LOWPOWERn for HDMI. Please, see the AM437x EVM's schematic.

I don't have HDMI on my board so do I need to enable a different GPIO?

In this case, no.

I can now get something to display on the screen during U-boot, but it looks like a really static-y version of the image that I am trying to display. Do you think this could be because I have the wrong values for the .pol_freq and or .divisor fields in the panel_config structure? I think I might have these values wrong

Most probably. Play with these values and check if there any improvement.

I tried playing around with those values and that didn't seem to help anything. Is there anything else you can think of that would be board/display specific that I might need to change?

What about splash.bmp.gz image? How did you create it? Is the image 24bits RGB?

Yes, it is a 24 bit RGB image. I created it by opening up a .png image in Paint and saving it as a .bmp image, and then I compressed it using gzip. I only have DSS_DATA bits 0 through 15 hooked up, will I still be able to use a 24-bit RGB image?

Never mind, I figured it out. I had to use LCD_INTERFACE_16_BIT for the data_lines field, but GFXFORMAT_RGB24_UNPACKED for the gfx_format field.

I have one more question: Is there a way to make the kernel not clear the display when it starts up?

Tanner Hunsucker73 said:

Is there a way to make the kernel not clear the display when it starts up?

So should I be able to add "ti,no-reset-on-init" to the dss node? Because if I try to add it I get a syntax error when I build the device tree

Tanner Hunsucker73 said:

So should I be able to add "ti,no-reset-on-init" to the dss node?

Where can I find that? And what should I be looking for?

The document is linked on the thread. This link.

Okay, so I am assuming I want to apply the "OMAPDSS: Adapt DSS driver for skipping initialization during bootup" patch, correct?

I am not sure which exact patch is the right patch. You will probably need to experiment with them.

Do I need to have a "skip_init" property in my dss node in the device tree?

You will, you have this patch applied.

So I have applied two patches: "OMAPDSS: Add methods for skipping display initialization" and "OMAPDSS: Adapt DSS driver for skipping initialization during bootup", and then I added "skip_init = <1>;" to my dss node in my device tree. But the display is still being cleared when the kernel boots up. Can you think of anything else that I am forgetting to do or that I need to add?

You can try to display the splash screen in the way that is implemented for AM57xx platform, if it is possible?

Is there any documentation that is specific to AM437x devices? This document is for DRA7x devices, and I have already found that the dss files that are modified in those patches are not the same ones I need to modify. 

Unfortunately, there is no such document for AM437x devices. There is only one community driver for AM335x, HYEONJAE CHOI's post for AM437x, and this DRA7x document.

Is there anyone at TI who would be able to help me get it figured out with the AM4378? There obviously has to be a way to get it to work, but I'm not familiar enough with the kernel to go digging through and try to figure out what changes I need to make.

U-Boot splash screen is not something that TI supports on their Processor SDK releases. Maybe in the future if I find a proper way to implement one will be able to help.