[PATCH AUTOSEL 5.15 04/24] arm64: dts: rockchip: fix rk3399-puma eMMC HS400 signal integrity

[Sasha Levin]

From: Jakob Unterwurzacher <jakob.unterwurzacher at theobroma-systems.com>

[ Upstream commit 62966cbdda8a92f82d966a45aa671e788b2006f7 ]

There are signal integrity issues running the eMMC at 200MHz on Puma
RK3399-Q7.

Similar to the work-around found for RK3399 Gru boards, lowering the
frequency to 100MHz made the eMMC much more stable, so let's lower the
frequency to 100MHz.

It might be possible to run at 150MHz as on RK3399 Gru boards but only
100MHz was extensively tested.

Cc: Quentin Schulz <foss+kernel at 0leil.net>
Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher at theobroma-systems.com>
Signed-off-by: Quentin Schulz <quentin.schulz at theobroma-systems.com>
Link: https://lore.kernel.org/r/20220119134948.1444965-1-quentin.schulz@theobroma-systems.com
Signed-off-by: Heiko Stuebner <heiko at sntech.de>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi b/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi
index 002ece51c3ba..08fa00364b42 100644
--- a/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi
+++ b/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi
@@ -439,6 +439,12 @@ usb3_id: usb3-id {
 };
 
 &sdhci {
+	/*
+	 * Signal integrity isn't great at 200MHz but 100MHz has proven stable
+	 * enough.
+	 */
+	max-frequency = <100000000>;
+
 	bus-width = <8>;
 	mmc-hs400-1_8v;
 	mmc-hs400-enhanced-strobe;
-- 
2.34.1