[RFC PATCH 0/4] Select the STM32MP25 LTDC pixel clock source for the RGB output

[Dario Binacchi <dario.binacchi@amarulasolutions.com>]

On STM32MP25 the LTDC pixel clock is selected in the SYSCFG
DISPLAYCLKCR register among the DSI byte lane clock, the LVDS PHY pixel
clock (reset value) and the LTDC kernel clock. The SYSCFG node is
already described as provider of this clock, which the LTDC references
as "ref" clock, but no driver registers it, so the RGB (DPI) output
can't work.

This series adds a driver for this mux, probed as an auxiliary device
of the STM32MP2 SYSCFG driver, and selects the pixel clock source on the
Engicam MicroGEA-STM32MP257D-RMM display overlays. Patch 1 is an
independent fix for the RGB display overlay.

Tested on the Engicam MicroGEA-STM32MP257D-RMM board with both the RGB
(Rocktech RK050HR345-CT106A) and the LVDS (Ampire AM-1280800W8TZQW-T00H)
displays.

I am sending it as RFC since I am not sure about:

- the mux parents are referenced by their global names. Should they
  rather be described by clocks/clock-names in the SYSCFG binding?
  Moreover, no driver registers "txbyteclk" yet.

- the pixel clock source is selected in the board devicetree by
  assigned-clock-parents. Should the LTDC driver rather select it
  according to its output (RGB, LVDS or DSI)?


Dario Binacchi (4):
  arm64: dts: st: fix the Engicam RMM RGB display pixel clock
  clk: stm32: add STM32MP25 SYSCFG clock driver
  soc: st: stm32mp2-syscfg: register the STM32MP25 clock device
  arm64: dts: st: select the Engicam RMM display pixel clock source

 ...gea-rmm-overlay-am-1280800w8tzqw-t00h.dtso |   3 +
 ...icrogea-rmm-overlay-rk050hr345-ct106a.dtso |   5 +
 drivers/clk/stm32/Kconfig                     |  12 ++
 drivers/clk/stm32/Makefile                    |   1 +
 drivers/clk/stm32/clk-stm32mp25-syscfg.c      | 111 ++++++++++++++++++
 drivers/soc/st/Kconfig                        |   1 +
 drivers/soc/st/stm32mp2-syscfg.c              |  28 ++++-
 7 files changed, 159 insertions(+), 2 deletions(-)
 create mode 100644 drivers/clk/stm32/clk-stm32mp25-syscfg.c

---
base-commit: 65ba8f34ec886ec72b2c07ddc8cf3d815c32869d
branch: stm32mp25-ltdc-pixclk

-- 
2.43.0