linux-kernel - [RFC PATCH 1/4] dts: phy: fix missing mdio device and probe failure of vsc8541-01 device

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Message-Id: <1588072608-7747-2-git-send-email-sagar.kadam@sifive.com>
Date:   Tue, 28 Apr 2020 04:16:45 -0700
From:   Sagar Shrikant Kadam <sagar.kadam@...ive.com>
To:     linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        robh+dt@...nel.org
Cc:     palmer@...belt.com, paul.walmsley@...ive.com, atish.patra@....com,
        devicetree@...r.kernel.org,
        Sagar Shrikant Kadam <sagar.kadam@...ive.com>
Subject: [RFC PATCH 1/4] dts: phy: fix missing mdio device and probe failure of vsc8541-01 device

HiFive unleashed A00 board has VSC8541-01 ethernet phy, this device is
identified as a Revision B device as described in device identification
registers. In order to use this phy in the unmanaged mode, it requires
a specific reset sequence of logical 0-1-0-1 transition on the NRESET pin
as documented here [1].

Currently, the bootloader (fsbl) takes care of the phy reset. If due to
some reason the phy device hasn't received the reset by the prior stages
before the linux macb driver comes into the picture, the MACB mii bus gets
probed but the mdio scan fails and is not even able to read the phy ID
registers. It gives an error message:

"libphy: MACB_mii_bus: probed
mdio_bus 10090000.ethernet-ffffffff: MDIO device at address 0 is missing."

Thus adding the device OUI (Organizationally Unique Identifier) to the phy
device node helps to probe the phy device.

[1]: VSC8541-01 datasheet:
https://www.mouser.com/ds/2/523/Microsemi_VSC8541-01_Datasheet_10496_V40-1148034.pdf

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@...ive.com>
---
 arch/riscv/boot/dts/sifive/hifive-unleashed-a00.dts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/boot/dts/sifive/hifive-unleashed-a00.dts b/arch/riscv/boot/dts/sifive/hifive-unleashed-a00.dts
index 4a2729f..60846e8 100644
--- a/arch/riscv/boot/dts/sifive/hifive-unleashed-a00.dts
+++ b/arch/riscv/boot/dts/sifive/hifive-unleashed-a00.dts
@@ -88,6 +88,7 @@
 	phy-mode = "gmii";
 	phy-handle = <&phy0>;
 	phy0: ethernet-phy@0 {
+		compatible = "ethernet-phy-id0007.0771";
 		reg = <0>;
 	};
 };
-- 
2.7.4