How does the LCD keep the uboot logo displayed to the kernel?

[longh]

Hi all:

    The chip I used is imx6sx, and the BSP version is 4.14.98,and the LCD drive mode is rgb565.Now I can display the logo in Uboot and kernel respectively, but during kernel startup, there will be a black screen around 3S, displaying the Linux logo.

    I have referred to this issue:

Patch to support uboot logo keep from uboot to kernel for NXP Linux and Android BSP (HDMI, LCD and L... Qiang Li - Mpu Se

    but the attachment cannot be downloaded, which indicates the error in the following figure:

[Rita_Wang]

We have same issue, I will do confirm it for you. And then give you update.

[longh]

Thank you very much. I am waiting for your reply

[Rita_Wang · Accepted solution]

Hi,

I have confirmed with our expert team, they said the patches above are based on IPU configuration you can not refer to. The i.mx6sx is based on LCDIF not IPU. So, when the kernel boot up you need to keep the LCDFI clock and the LCDIF configurations no changes. And when the Display diver register, keeping the LCDIF setting with no changes. Hope this can do help for you.(6SX是基于LCDIF的，不是IPU的，在kernel启动的过程中，要保持LCDIF的clock还有LCDIF的设置不能改变。

Display driver注册的时候，不进行LCDIF的重设。)

Have a nice day

Rita

[longh]

    Thanks for your reply, I have completed the implementation of this function.The following is the general implementation process.It may be helpful to some people.

    In u-boot 2018.03, you need to properly configure the parameters of the LCD and then mask lcdif_power_down() called in cpu.c.

    In the 4.14.98 kernel, mxsfb.c needs to be modified by calling pm_runtime_get_sync(&host->pdev->dev) in the probe function.Make sure the following clock is on and block all register initializations, then map the fb address to uboot.

imx_clk_prepare_enable (CLKS [IMX6SX_CLK_LCDIF1_PIX]);

imx_clk_prepare_enable  (CLKS [IMX6SX_CLK_LCDIF_APB]);

imx_clk_prepare_enable (CLKS [IMX6SX_CLK_AXI]);

imx_clk_prepare_enable (CLKS [IMX6SX_CLK_DISPLAY_AXI]);

[Rita_Wang]

Good, thanks a lot for your sharing~~

[zhenhua_lin]

Does any update for imx6ull of this feature ?

[longh]

If you want to keep the screen from flickering, you also need to configure PWM in uboot and modify the PWM -backlight.c in the kernel to avoid reinitializing the registers

[zhenhua_lin]

Could you please share your patch?