AM4378: custom LCD panel configuration in u-boot.

Hi Harsha,
There's an earlier guide on how to add u-boot splash screen
software-dl.ti.com/.../Foundational_Components_U-Boot.html
Hope it will help you add LCD panel configuration in u-boot.
Best,
-Hong

Hi Hong,

The one you are referring is for AM335X which does not use DSS module.

But in the case of AM437X it contains a DSS module which needs to be configured according to custom LCD configurations. So this does not work for me.

Thanks for the reply !

Hi Harsha,
For your reference, there's a link on kernel driver (omapdrm) for DSS
software-dl.ti.com/.../DSS.html
omapdrm is a Direct Rendering Manager (DRM) driver, located in the kernel directory drivers/gpu/drm/omapdrm/
But I'm not aware of such support in u-boot.

One reference on u-boot splash screen is e2e.ti.com/.../2592257

Best,
-Hong

Hi Hong,

I have gone through this reference link : software-dl.ti.com/.../DSS.html. It is about the DSS module

,but I'm stuck with the DSS module configurations. 

I have referred this link : e2e.ti.com/.../2592257 to enable LCD support in u-boot. My concern is related to the timing parameters that need to be configured according to the LCD panel.

Please let me know if there are any references related to the timing parameters calculations.

Thanks for the reply !

Hi Harsha,
Please note that porting work referenced in the below link was developed by community member.
e2e.ti.com/.../2592257
From code snippet below, panel_cfg structure elements needs to be configured first based on LCD panel, and then written into the
corresponding DSS_DISPC registers as described in more details in Table 13-41. DSS_DISPC Registers of AM437x TRM

        writel(panel_cfg->timing_h, &dispc->timing_h);
        writel(panel_cfg->timing_v, &dispc->timing_v);
        writel(panel_cfg->pol_freq, &dispc->pol_freq);
        writel(panel_cfg->divisor, &dispc->divisor);
        writel(panel_cfg->lcd_size, &dispc->size_lcd);
        writel(panel_cfg->load_mode << LOADMODE_SHIFT, &dispc->config);
        writel( GP_OUT0 | GP_OUT1 |
                panel_cfg->panel_type << TFTSTN_SHIFT |
                panel_cfg->data_lines << DATALINES_SHIFT, &dispc->control);
        writel(panel_cfg->panel_color, &dispc->default_color0);
        writel((u32) panel_cfg->frame_buffer, &dispc->gfx_ba0);
        writel((u32) panel_cfg->frame_buffer, &dispc->gfx_ba1);

Best,

-Hong

Hi Hong,

I have tried to configure the panel_cfg structure according to my LCD timing parameters that I mentioned earlier. 

But there are no references to the calculations of the writel(panel_cfg->divisor, &dispc->divisor); 

I'm stuck with the LCD panel frequency configuration. Most of the other parameters I have configured in the DISPC  Register.

Please let me know if there are any references related to the timing parameters calculations.

Thanks for the reply !

Hi Harsha,
My understanding from your original post is your LCD panel display works in the kernel.
If that is the case, one option for you to set-up the panel_cfg structure in u-boot for your LCD panel is "dump" DSS_DISPC registers after kernel up.
I'm attaching the screen-shot on DSS_DISPC registers captured via T32 JTAG debugger on AM437x GP EVM after the kernel up running.
Alternative is reading DSS_DISPC registers via devmem2 @kernel prompt.
For example, reading DISPC_DIVISOR register @0x4832A470 is listed below for your reference:

root@am437x-evm:~# devmem2 0x4832a470
/dev/mem opened.
Memory mapped at address 0xb6ff5000.
Read at address  0x4832A470 (0xb6ff5470): 0x00010006

Best,

-Hong

Hi Hong,

This helped me to solve the panel configuration issue. But still I don't see anything on the display I see a blank display.

I think this issue is related to frame buffer. I have tried writing data to the frame buffer with the mw.w u-boot command I didn't see any of it reflected on the LCD.

Can you please let know if you have any suggestion related to this issue.

Thanks for the reply !