u-boot 2021.04: Add LCD support

[hansemro]

References:

• https://github.com/KFire-Android/kf_u-boot/blob/p-ti-u-boot-2013.04/board/ti/omap4_kc1/kc1_panel.c
• https://github.com/KFire-Android/kf_u-boot/blob/p-ti-u-boot-2013.04/board/ti/omap4_kc1/kc1_panel.h
• https://github.com/KFire-Android/kf_u-boot/blob/2b71480b86be5180c6d10f6d8014ee42d3318b83/board/ti/omap4_kc1/omap4_spi.c#L265-L452

Tasks:

• use omap3_spi driver in place of downstream omap4_spi driver.
  • move LCD panel node under mcspi4 in device tree (omap4-kc1-dss.dtsi)
  • create UCLASS_DISPLAY driver that probes LCD panel node and initializes display via spi. (drivers/video/amazon/kc1_panel.c)
    • probe display from DT
    • add LCD init/enable sequence for multiple LCD vendors
    • handle KC1 mbid ??? For now, it is just set to 0.
  • create UCLASS_PWM driver for GPTimer/dmtimer (drivers/pwm/pwm-ti-dmtimer.c)
    • create stub driver to probe DMTimer-1ms (drivers/clk/ti-dm.c)
      • add compatibility for ti,omap3430-timer
    • use device tree compatibility ID to determine revision or use same check in linux driver
    • implement set_invert
    • implement set_config
    • implement enable
• working LCD in Linux

[hansemro]

LCD backlight driver + PWM driver are mostly implemented in https://github.com/hansemro/kf_u-boot/tree/2021.04_omap4_dss_pwm_dev

To use backlight, run hush command: kc1panel (Removed after implementing working omap4_dss driver)

[hansemro]

Current issue faced in 332d9b2: KC1 panel fails to work after booting into Linux kernel.

When Linux kernel probes display, LCD panel and backlight go off. After a few moments, only backlight comes back up.

I am uncertain whether this is a kernel or DT or u-boot issue. With that said, u-boot in 2021.04_dss_poc_dm_hack branch does not exhibit this issue.