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From: Sean Anderson <sanderson@brivo.com>
To: Neil Armstrong <neil.armstrong@linaro.org>,
	Kevin Hilman <khilman@baylibre.com>,
	linux-arm-kernel@lists.infradead.org
Cc: linux-amlogic@lists.infradead.org,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	linux-kernel@vger.kernel.org, Rob Herring <robh@kernel.org>,
	devicetree@vger.kernel.org, Conor Dooley <conor+dt@kernel.org>,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
	Jerome Brunet <jbrunet@baylibre.com>,
	Sean Anderson <sanderson@brivo.com>
Subject: [PATCH] arm64: dts: amlogic: meson-s4: Set stdout-path to uart_b
Date: Tue, 29 Sep 2026 12:34:10 -0400	[thread overview]
Message-ID: <20260929163457.3237394-1-sanderson@brivo.com> (raw)

If stdout-path is not set then bootloaders such as U-Boot may fail to
boot when they cannot find the serial console. Normally, this would be
added to the board devicetree, but in this case the boot ROM,
first-stage bootloader, ATF, and TEE all use this serial port with this
baud rate [1]. All of the listed components are signed by Amlogic and can't
be modified by OEMs. So while someone might want to use a different
port, they can't prevent previous stages of the boot process from
printing to this port. Therefore, set the serial port in the SoC
devicetree. Boards can override it in their devicetree if necessary.

[1] Actually, the baud rate used by the ROM et al. is 888888, but some
    userspace tools (such as agetty) choke on non-standard baud rates,
    so we use 921600 which is close enough for most serial adapters.

Signed-off-by: Sean Anderson <sanderson@brivo.com>
---

 arch/arm64/boot/dts/amlogic/meson-s4-s805x2-aq222.dts    | 8 --------
 .../boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts    | 5 -----
 arch/arm64/boot/dts/amlogic/meson-s4.dtsi                | 9 ++++++++-
 3 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/boot/dts/amlogic/meson-s4-s805x2-aq222.dts b/arch/arm64/boot/dts/amlogic/meson-s4-s805x2-aq222.dts
index 0a3f81ea0fb0a..15bf143317a2d 100644
--- a/arch/arm64/boot/dts/amlogic/meson-s4-s805x2-aq222.dts
+++ b/arch/arm64/boot/dts/amlogic/meson-s4-s805x2-aq222.dts
@@ -14,10 +14,6 @@ / {
 	#address-cells = <2>;
 	#size-cells = <2>;
 
-	aliases {
-		serial0 = &uart_b;
-	};
-
 	memory@0 {
 		device_type = "memory";
 		reg = <0x0 0x0 0x0 0x40000000>;
@@ -141,10 +137,6 @@ &pwm_ij {
 	status = "okay";
 };
 
-&uart_b {
-	status = "okay";
-};
-
 &ir {
 	status = "okay";
 	pinctrl-0 = <&remote_pins>;
diff --git a/arch/arm64/boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts b/arch/arm64/boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts
index 99d5df71b9cd4..c602091bca0a6 100644
--- a/arch/arm64/boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts
+++ b/arch/arm64/boot/dts/amlogic/meson-s4-s905y4-khadas-vim1s.dts
@@ -22,7 +22,6 @@ aliases {
 		mmc2 = &sdio; /* SDIO */
 		rtc0 = &rtc;
 		rtc1 = &vrtc;
-		serial0 = &uart_b;
 	};
 
 	memory@0 {
@@ -334,7 +333,3 @@ bluetooth {
 		clock-names = "lpo";
 	};
 };
-
-&uart_b {
-	status = "okay";
-};
diff --git a/arch/arm64/boot/dts/amlogic/meson-s4.dtsi b/arch/arm64/boot/dts/amlogic/meson-s4.dtsi
index 2a6fbd5308362..3e432e232a76a 100644
--- a/arch/arm64/boot/dts/amlogic/meson-s4.dtsi
+++ b/arch/arm64/boot/dts/amlogic/meson-s4.dtsi
@@ -13,6 +13,14 @@
 #include <dt-bindings/reset/amlogic,meson-s4-reset.h>
 
 / {
+	aliases {
+		serial0 = &uart_b;
+	};
+
+	chosen {
+		stdout-path = "serial0:921600n8";
+	};
+
 	cpus {
 		#address-cells = <2>;
 		#size-cells = <0>;
@@ -794,7 +802,6 @@ uart_b: serial@7a000 {
 				interrupts = <GIC_SPI 169 IRQ_TYPE_EDGE_RISING>;
 				clocks = <&xtal>, <&clkc_periphs CLKID_UART_B>, <&xtal>;
 				clock-names = "xtal", "pclk", "baud";
-				status = "disabled";
 			};
 
 			reset: reset-controller@2000 {
---
base-commit: 6f8319e3e9a44dd537d17f41565a8453c560a581
branch: s4_stdout

-- 
2.53.0


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                 reply	other threads:[~2026-09-29 16:35 UTC|newest]

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