linux-kernel - [PATCH v2] arm64: dts: rockchip: Set RK3399-Gru PCLK

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Date:   Tue, 30 Aug 2022 13:16:17 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Heiko Stuebner <heiko@...ech.de>
Cc:     linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        zain wang <wzz@...k-chips.com>, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Lin Huang <hl@...k-chips.com>,
        Brian Norris <briannorris@...omium.org>
Subject: [PATCH v2] arm64: dts: rockchip: Set RK3399-Gru PCLK_EDP to 24 MHz

From: zain wang <wzz@...k-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@...omium.org>
Signed-off-by: zain wang <wzz@...k-chips.com>
Signed-off-by: Brian Norris <briannorris@...omium.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