arm64: dts: rockchip: Set RK3399-Gru PCLK_EDP to 24 MHz

We've found the AUX channel to be less reliable with PCLK_EDP at a
higher rate (typically 25 MHz). This is especially important on systems
with PSR-enabled panels (like Gru-Kevin), since we make heavy, constant
use of AUX.

According to Rockchip, using any rate other than 24 MHz can cause
"problems between syncing the PHY an PCLK", which leads to all sorts of
unreliabilities around register operations.

Fixes: d67a38c ("arm64: dts: rockchip: move core edp from rk3399-kevin to shared chromebook")
Reviewed-by: Douglas Anderson <[email protected]>
Signed-off-by: zain wang <[email protected]>
Signed-off-by: Brian Norris <[email protected]>
Link: https://lore.kernel.org/r/20220830131212.v2.1.I98d30623f13b785ca77094d0c0fd4339550553b6@changeid
Signed-off-by: Heiko Stuebner <[email protected]>

Author: zainwangrockchips

arch/arm64/boot/dts/rockchip/rk3399-gru-chromebook.dtsi

@@ -244,6 +244,14 @@
 &edp {
 	status = "okay";
 
+	/*
+	 * eDP PHY/clk don't sync reliably at anything other than 24 MHz. Only
+	 * set this here, because rk3399-gru.dtsi ensures we can generate this
+	 * off GPLL=600MHz, whereas some other RK3399 boards may not.
+	 */
+	assigned-clocks = <&cru PCLK_EDP>;
+	assigned-clock-rates = <24000000>;
+
 	ports {
 		edp_out: port@1 {
 			reg = <1>;