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From:   Christoph Muellner <christoph.muellner@theobroma-systems.com>
To:     robh+dt@kernel.org, mark.rutland@arm.com, heiko@sntech.de,
        shawn.lin@rock-chips.com
Cc:     Christoph Muellner <christoph.muellner@theobroma-systems.com>,
        Philipp Tomsich <philipp.tomsich@theobroma-systems.com>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        Brian Norris <briannorris@chromium.org>,
        Klaus Goger <klaus.goger@theobroma-systems.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Douglas Anderson <dianders@chromium.org>,
        Matthias Brugger <mbrugger@suse.com>,
        Randy Li <ayaka@soulik.info>,
        Tony Xie <tony.xie@rock-chips.com>,
        Vicente Bergas <vicencb@gmail.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-rockchip@lists.infradead.org
Subject: [PATCH v3 4/4] arm64: dts: rockchip: Decrease emmc-phy's drive impedance on rk3399-puma
Date:   Fri, 22 Mar 2019 12:34:53 +0100
Message-Id: <20190322113456.16324-4-christoph.muellner@theobroma-systems.com>
In-Reply-To: <20190322113456.16324-1-christoph.muellner@theobroma-systems.com>
References: <20190322113456.16324-1-christoph.muellner@theobroma-systems.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@theobroma-systems.com>
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>
Tested-by: Klaus Goger <klaus.goger@theobroma-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