From: zain wang <wzz@rock-chips.com>

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.

Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: zain wang <wzz@rock-chips.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>
---

Changes in v2:
 * Add Doug's reviewed-by
 * Set authorship correctly

 arch/arm64/boot/dts/rockchip/rk3399-gru-chromebook.dtsi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/boot/dts/rockchip/rk3399-gru-chromebook.dtsi b/arch/arm64/boot/dts/rockchip/rk3399-gru-chromebook.dtsi
index 45796b9fd94f..ee6095baba4d 100644
--- a/arch/arm64/boot/dts/rockchip/rk3399-gru-chromebook.dtsi
+++ b/arch/arm64/boot/dts/rockchip/rk3399-gru-chromebook.dtsi
@@ -244,6 +244,14 @@ &dmc {
 &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>;
-- 
2.37.2.672.g94769d06f0-goog

On Tue, 30 Aug 2022 13:16:17 -0700, Brian Norris wrote:
> 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.

Applied, thanks!

[1/1] arm64: dts: rockchip: Set RK3399-Gru PCLK_EDP to 24 MHz
      commit: 8123437cf46ea5a0f6ca5cb3c528d8b6db97b9c2

Best regards,
-- 
Heiko Stuebner <heiko@sntech.de>