I recently ordered 2 evaluation kits for your PicoCore MX7ULP and these came with a 3.5" LCD touchscreen (SKU: B.LCD.22).
Before starting customization of the image and deploy self-compiled binaries, I wanted to try the default factory-installed image first. I could successfully start the image and get to a console over the serial line but nothing is displayed on the attached LCD screen, even if I can see that an X server is started and running with a matchbox window manager on top of it as shown in following output of ps command:
- # ps
- PID USER VSZ STAT COMMAND
- 1 root 2604 S init
- 264 root 0 SW< [MWIFIEX_DFS_CHS]
- 271 root 3368 S xinit /usr/bin/matchbox-session -- /usr/bin/X :0 vt0
- 272 root 71140 S< /usr/bin/X :0 vt02 -auth //.serverauth.235
- 275 root 8076 S matchbox-window-manager
- 276 root 12032 S matchbox-desktop
- 277 root 8576 S matchbox-panel --orientation south --no-session --de
- 278 root 6888 S mb-applet-launcher matchbox-keyboard.png matchbox-ke
- 281 root 7572 S mb-applet-menu-launcher
- 282 root 7592 S mb-applet-clock
Looking at the device tree from U-Boot I see that the lcd_panel in mipi_dsi device is configured for another LCD display "TIANMA_PANEL_TM050JDHG33" that is definitely not matching the specs of your reference B.LCD.22 screen shipped with evaluation kits.
compatible = "fsl,imx7ulp-mipi-dsi";
reg = <0x40a90000 0x00010000>;
interrupts = <0x00000000 0x0000002e 0x00000004>;
clocks = <0x00000002 0x00000047>;
clock-names = "mipi_dsi_clk";
data-lanes-num = <0x00000002>;
phy-ref-clkfreq = <0x016e3600>;
max-data-rate = <0x2faf0800>;
sim = <0x00000010>;
status = "okay";
pinctrl-names = "default", "sleep";
pinctrl-0 = <0x00000021>;
pinctrl-1 = <0x00000021>;
lcd_panel = "TIANMA_PANEL_TM050JDHG33";
resets = <0x00000022>;
Further looking in the MIPI DSI driver of iMX7ULP (drivers/video/fbdev/mxc/mipi_dsi_northwest.c from Buildroot release fsimx7ulp-B2019.12) I see that other LCD panels are supported but none seem to match your 3.5" LCD.
1. Could you please provide a compatible compiled DTB that would work with your factory image installed on evaluation kit ?
2. Could you provide updated sources that would allow me to later compile my own kernel with support for your B.LCD.22 LCD screen including touch support ?
If you have any detailed documentation on the integration of this screen on the system, I would be interested (cabling, configuration in Linux kernel, enabling/disabling backlight, ...).
Thanks for your support,