[PATCH] Eliminate Odroid HC4 power glitches during boot.

[Neil Armstrong]

Hi,

On 1/17/26 05:02, Eric Neulight via B4 Relay wrote:
> From: Eric Neulight <Eric.Neulight at linuxdev.slmail.me>
> 
> Fix issue with Odroid HC4 (and all meson-sm1-odroid) DTS that causes
> regulator power to momentarily glitch OFF-ON during boot.  Add
> regulator-boot-on to all regulator-fixed and regulator-gpio entries
> that (1) define a gpio AND (2) define regulator-always-on.
> 
> U-boot powers on devices necessary for boot then hands off the DTB to
> the kernel.  During probe, linux drivers/regulator/fixed.c and
> gpio-regulator.c both first set the regulator control gpio (that U-boot
> already turned ON) to default OFF before then setting it to the defined
> (ON) state. This glitches the power to the affected devices, unless
> regulator-boot-on is specified with it.  In fact, U-boot has the same
> behavior.  So, during reboot, a power glitch can actually happen twice:
> once when U-boot reads the DTB and probes the gpio and again when the
> kernel reads the DTB and probes the gpio.
> 
> Problem this fixes: On the Odroid HC4, power to the SATA ports glitches
> during boot and causes some HDDs to do emergency head retract, which
> should be avoided.  On the HC4, power glitches to the SD card, USB,
> SATA, and HDMI interfaces during boot.  These are all boot devices.
> A power glitch can potentially cause a problem for any sensitive devices
> during boot.
> 
> NOTE: This is not limited to just the HC4, likely an issue with ALL DTS
> with regulator-fixed or regulator-gpio entries that (1) define a gpio
> AND (2) define regulator-always-on.  All such entries should also
> include regulator-boot-on in order to avoid potential power glitches.
> At worst, adding regulator-boot-on in such cases is harmless because of
> regulator-always-on, and, at best, it eliminates detrimental power
> glitches during boot.  So, this is best-practice.
> 
> Fixes: 164147f094ec5d0fc2c2098a888f4b50cf3096a7 ("arm64: dts: meson-sm1-odroid-hc4: add regulators controlled by GPIOH_8")
> Fixes: 45d736ab17b44257e15e75e0dba364139fdb0983 ("arm64: dts: meson-sm1-odroid: add 5v regulator gpio")
> Fixes: 1f80a5cf74a60997b92d2cde772edec093bec4d9 ("arm64: dts: meson-sm1-odroid: add missing enable gpio and supply for tf_io regulator")
> Fixes: 88d537bc92ca035e2a9920b0abc750dd62146520 ("arm64: dts: meson: convert meson-sm1-odroid-c4 to dtsi")
> 
> Signed-off-by: Eric Neulight <Eric.Neulight at linuxdev.slmail.me>
> ---
>   arch/arm64/boot/dts/amlogic/meson-sm1-odroid-hc4.dts | 2 ++
>   arch/arm64/boot/dts/amlogic/meson-sm1-odroid.dtsi    | 3 +++
>   2 files changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/amlogic/meson-sm1-odroid-hc4.dts b/arch/arm64/boot/dts/amlogic/meson-sm1-odroid-hc4.dts
> index 0170139b8d32f4274ad991b0f3d9a0f6c67969ce..3ece30a0a1fff736c544cf89ed0a8cca0890f128 100644
> --- a/arch/arm64/boot/dts/amlogic/meson-sm1-odroid-hc4.dts
> +++ b/arch/arm64/boot/dts/amlogic/meson-sm1-odroid-hc4.dts
> @@ -52,6 +52,7 @@ p12v_0: regulator-p12v-0 {
>   
>   		gpio = <&gpio GPIOH_8 GPIO_OPEN_DRAIN>;
>   		enable-active-high;
> +		regulator-boot-on;
>   		regulator-always-on;
>   	};
>   
> @@ -65,6 +66,7 @@ p12v_1: regulator-p12v-1 {
>   
>   		gpio = <&gpio GPIOH_8 GPIO_OPEN_DRAIN>;
>   		enable-active-high;
> +		regulator-boot-on;
>   		regulator-always-on;
>   	};
>   
> diff --git a/arch/arm64/boot/dts/amlogic/meson-sm1-odroid.dtsi b/arch/arm64/boot/dts/amlogic/meson-sm1-odroid.dtsi
> index c4524eb4f0996dfbccec16ca5b936a5c3b2663a5..0bce4e8d965f2c83e6ba677fef2ede2726de6ed1 100644
> --- a/arch/arm64/boot/dts/amlogic/meson-sm1-odroid.dtsi
> +++ b/arch/arm64/boot/dts/amlogic/meson-sm1-odroid.dtsi
> @@ -37,6 +37,7 @@ tflash_vdd: regulator-tflash-vdd {
>   
>   		gpio = <&gpio_ao GPIOAO_3 GPIO_OPEN_DRAIN>;
>   		enable-active-high;
> +		regulator-boot-on;
>   		regulator-always-on;
>   	};
>   
> @@ -50,6 +51,7 @@ tf_io: gpio-regulator-tf-io {
>   
>   		enable-gpios = <&gpio_ao GPIOE_2 GPIO_OPEN_DRAIN>;
>   		enable-active-high;
> +		regulator-boot-on;
>   		regulator-always-on;
>   
>   		gpios = <&gpio_ao GPIOAO_6 GPIO_OPEN_SOURCE>;
> @@ -81,6 +83,7 @@ vcc_5v: regulator-vcc-5v {
>   		regulator-name = "5V";
>   		regulator-min-microvolt = <5000000>;
>   		regulator-max-microvolt = <5000000>;
> +		regulator-boot-on;
>   		regulator-always-on;
>   		vin-supply = <&main_12v>;
>   		gpio = <&gpio GPIOH_8 GPIO_OPEN_DRAIN>;
> 
> ---
> base-commit: b71e635feefc852405b14620a7fc58c4c80c0f73
> change-id: 20260116-odroid-hc4-dts-54f4254d8554
> 
> Best regards,

Reviewed-by: Neil Armstrong <neil.armstrong at linaro.org>

Thanks,
Neil