linux-kernel - [PATCH v2] ARM: dts: imx6qdl-sr-som: Increase the PHY reset duration to 10ms

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Message-Id: <20210625121353.3698240-1-maxime.chevallier@bootlin.com>
Date:   Fri, 25 Jun 2021 14:13:53 +0200
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     Russell King <linux@...linux.org.uk>,
        Shawn Guo <shawnguo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        thomas.petazzoni@...tlin.com, herve.codina@...tlin.com,
        devicetree@...r.kernel.org
Cc:     Maxime Chevallier <maxime.chevallier@...tlin.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] ARM: dts: imx6qdl-sr-som: Increase the PHY reset duration to 10ms

The AR803x PHY used on this modules seems to require the reset line to
be asserted for around 10ms in order to avoid rare cases where the PHY
gets stuck in an incoherent state that prevents it to function
correctly.

The previous value of 2ms was found to be problematic on some setups,
causing intermittent issues where the PHY would be unresponsive
every once in a while on some sytems, with a low occurrence (it typically
took around 30 consecutive reboots to encounter the issue).

Bumping the delay to the 10ms makes the issue dissapear, with more than
2500 consecutive reboots performed without the issue showing-up.

Fixes: 208d7baf8085 ("ARM: imx: initial SolidRun HummingBoard support")
Signed-off-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
Tested-by: Hervé Codina <herve.codina@...tlin.com>
---
This V2 was quickly resent, since the commit-log was incorrect.

v2 : Reworded the commit-log to remove an incorrect mention of the
datasheet. Add a comment to the DT to explicitly explain the issue.

 arch/arm/boot/dts/imx6qdl-sr-som.dtsi | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/imx6qdl-sr-som.dtsi b/arch/arm/boot/dts/imx6qdl-sr-som.dtsi
index 0ad8ccde0cf8..f86efd0ccc40 100644
--- a/arch/arm/boot/dts/imx6qdl-sr-som.dtsi
+++ b/arch/arm/boot/dts/imx6qdl-sr-som.dtsi
@@ -54,7 +54,13 @@ &fec {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_microsom_enet_ar8035>;
 	phy-mode = "rgmii-id";
-	phy-reset-duration = <2>;
+
+	/*
+	 * The PHY seems to require a long-enough reset duration to avoid
+	 * some rare issues where the PHY gets stuck in an inconsistent and
+	 * non-functional state at boot-up. 10ms proved to be fine .
+	 */
+	phy-reset-duration = <10>;
 	phy-reset-gpios = <&gpio4 15 GPIO_ACTIVE_LOW>;
 	status = "okay";

-- 
2.25.4