[RFC PATCH 1/4] arm64: dts: st: fix the Engicam RMM RGB display pixel clock

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

On STM32MP255/257 the LTDC "lcd" clock is a fixed placeholder, since
with the LVDS output the pixel clock comes from the LVDS PHY. With the
RGB output the pixel clock is instead the LTDC kernel clock
(ck_ker_ltdc). Since no consumer references it, the clock is turned off
by clk_disable_unused() and its rate is never set. As a result, the LTDC
does not run and every commit times out:

  [CRTC:42:crtc-0] vblank wait timed out
  [drm] *ERROR* flip_done timed out

Use ck_ker_ltdc as "lcd" clock for the RGB panel overlay.

Fixes: bc7b07bda4e0 ("arm64: dts: st: support Engicam MicroGEA-STM32MP257D-RMM board")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
---

 ...2mp257d-engicam-microgea-rmm-overlay-rk050hr345-ct106a.dtso | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/boot/dts/st/stm32mp257d-engicam-microgea-rmm-overlay-rk050hr345-ct106a.dtso b/arch/arm64/boot/dts/st/stm32mp257d-engicam-microgea-rmm-overlay-rk050hr345-ct106a.dtso
index f89641bdb23b..7be955be58ed 100644
--- a/arch/arm64/boot/dts/st/stm32mp257d-engicam-microgea-rmm-overlay-rk050hr345-ct106a.dtso
+++ b/arch/arm64/boot/dts/st/stm32mp257d-engicam-microgea-rmm-overlay-rk050hr345-ct106a.dtso
@@ -10,6 +10,7 @@
 /dts-v1/;
 /plugin/;
 
+#include <dt-bindings/clock/st,stm32mp25-rcc.h>
 #include <dt-bindings/gpio/gpio.h>
 #include <dt-bindings/interrupt-controller/irq.h>
 
@@ -35,6 +36,8 @@ touchscreen@38 {
 };
 
 &ltdc {
+	/* RGB output: the pixel clock is the LTDC kernel clock */
+	clocks = <&rcc CK_KER_LTDC>, <&rcc CK_BUS_LTDC>, <&syscfg>, <&lvds>;
 	pinctrl-names = "default", "sleep";
 	pinctrl-0 = <&ltdc_pins_a>;
 	pinctrl-1 = <&ltdc_sleep_pins_a>;
-- 
2.43.0