linux-kernel - [PATCH v3 4/4] arm64: dts: rockchip: Decrease emmc-phy's drive impedance on rk3399-puma

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Message-Id: <20190322113456.16324-4-christoph.muellner@theobroma-systems.com>
Date:   Fri, 22 Mar 2019 12:34:53 +0100
From:   Christoph Muellner <christoph.muellner@...obroma-systems.com>
To:     robh+dt@...nel.org, mark.rutland@....com, heiko@...ech.de,
        shawn.lin@...k-chips.com
Cc:     Christoph Muellner <christoph.muellner@...obroma-systems.com>,
        Philipp Tomsich <philipp.tomsich@...obroma-systems.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Brian Norris <briannorris@...omium.org>,
        Klaus Goger <klaus.goger@...obroma-systems.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Matthias Brugger <mbrugger@...e.com>,
        Randy Li <ayaka@...lik.info>,
        Tony Xie <tony.xie@...k-chips.com>,
        Vicente Bergas <vicencb@...il.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org
Subject: [PATCH v3 4/4] arm64: dts: rockchip: Decrease emmc-phy's drive impedance on rk3399-puma

The RK3399-Q7 (Puma) requires 33 Ohm drive strength to ensure signal
integrity at HS-400 (200MHz clock, DDR signalling).

A repeated EMC testing run validates that this increase does not
negatively impact EMC compliance (emissions have ample distance to
the regulatory limits).

Signed-off-by: Christoph Muellner <christoph.muellner@...obroma-systems.com>
Signed-off-by: Philipp Tomsich <philipp.tomsich@...obroma-systems.com>
Tested-by: Jakob Unterwurzacher <jakob.unterwurzacher@...obroma-systems.com>
Tested-by: Klaus Goger <klaus.goger@...obroma-systems.com>
---
 arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi b/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi
index 0130b9f98c9d..4f75bb6b2f14 100644
--- a/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi
+++ b/arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi
@@ -146,6 +146,7 @@
 
 &emmc_phy {
 	status = "okay";
+	drive-impedance-ohm = <33>;
 };
 
 &gmac {
-- 
2.11.0