Re: [PATCH 2/2] arm64: dts: exynos: Add initial support for Samsung Galaxy Watch FE

[Aiden Isik]

On Monday, August 17th, 2026 at 11:37 AM, Aiden Isik via B4 Relay <devnull+aidenisik.member.fsf.org@xxxxxxxxxx> wrote:

> From: Aiden Isik <aidenisik@xxxxxxxxxxxxxx>
> 
> The Samsung Galaxy Watch FE (SM-R861/SM-R866), codenamed lucky7, is a
> smartwatch developed by Samsung and released in 2024. It has 1.5GiB RAM,
> 16GiB of eMMC storage, an Exynos5515 (W920) SoC, and a 396x396 display.
> 
> Support for the following is added by this device tree:
> - Bootloader framebuffer
> - Memory
> 
> Only the lowest 490MiB and highest 512MiB of memory are used for now.
> The 488MiB between the addresses of 0x9ea00000 and 0xbe680000 is excluded
> from the memory node due to a bug where if the kernel even knows about
> the existence of this memory, one or both cores will lock up and cause
> an RCU stall.

This used to work fine on my 7.0 and 7.1-based branches, so I did a bit
of bisecting and found that the issue was introduced in commit
7b9f263909a57e2463c6a543d72651e00a3fd0d6
(of: reserved_mem: only support one <base size> entry in reg property).

This explains why hiding the memory from the kernel worked, I *was*
reserving this memory but in a way which this commit discontinued.

I initially thought this was some randomly-occurring "heisenbug", which
is why I submitted the memory-hiding fix instead as it definitely worked,
but now I know the real problem I will fix the reserved-memory node.

I will fix this in the next version of this patchset, next merge window.

> 
> Signed-off-by: Aiden Isik <aidenisik+git@xxxxxxxxxxxxxx>
> ---
>  arch/arm64/boot/dts/exynos/exynos5515-lucky7.dts | 106 +++++++++++++++++++++++
>  1 file changed, 106 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/exynos/exynos5515-lucky7.dts b/arch/arm64/boot/dts/exynos/exynos5515-lucky7.dts
> new file mode 100644
> index 000000000000..f91ea7e44cf8
> --- /dev/null
> +++ b/arch/arm64/boot/dts/exynos/exynos5515-lucky7.dts
> @@ -0,0 +1,106 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Samsung Galaxy Watch FE (lucky7/SM-R861/SM-R866) device tree source
> + *
> + * Copyright (c) 2026 Aiden Isik <aidenisik+git@xxxxxxxxxxxxxx>
> + */
> +
> +/dts-v1/;
> +#include "exynos5515.dtsi"
> +
> +/ {
> +	compatible = "samsung,lucky7", "samsung,exynos5515";
> +	chassis-type = "watch";
> +	model = "Samsung Galaxy Watch FE (SM-R861/SM-R866)";
> +
> +	chosen {
> +		ranges;
> +		#address-cells = <2>;
> +		#size-cells = <1>;
> +
> +		framebuffer@9e0cf000 {
> +			compatible = "simple-framebuffer";
> +			reg = <0x0 0x9e0cf000 (396 * 396 * 4)>;
> +			format = "a8r8g8b8";
> +			height = <396>;
> +			stride = <(396 * 4)>;
> +			width = <396>;
> +		};
> +	};
> +
> +	memory@80000000 {
> +		/*
> +		 * Use the lowest 490MiB and highest 512MiB of memory.
> +		 * The 488MiB between the addresses of 0x9ea00000 and
> +		 * 0xbe680000 is currently unused due to any memory accesses
> +		 * in several ranges between those addresses causing the core
> +		 * performing the accesses to stall.
> +		 */
> +		reg = <0x0 0x80000000 0x1ea00000>,
> +		      /* Crashing memory at 0x9ea00000-0xbe680000 */
> +		      /* Memory hole at 0xbe680000-0xc0000000 */
> +		      <0x0 0xc0000000 0x20000000>;
> +		device_type = "memory";
> +	};
> +
> +	reserved-memory {
> +		ranges;
> +		#address-cells = <2>;
> +		#size-cells = <1>;
> +
> +		framebuffer@9e0cf000 {
> +			reg = <0x0 0x9e0cf000 (396 * 396 * 4)>;
> +			no-map;
> +		};
> +
> +		misc-rmem {
> +			/*
> +			 * Some of these regions belong to memory-mapped
> +			 * devices, and will be assigned to drivers as support
> +			 * is added.
> +			 *
> +			 * Other regions belong to the TrustZone firmware
> +			 * and should never be touched.
> +			 */
> +			reg = <0x0 0x87000000 0x200000>,
> +			      <0x0 0x87fff000 0x1000>,
> +			      <0x0 0x8a000000 0x31000>,
> +			      <0x0 0x8d800000 0x180000>,
> +			      <0x0 0x8ffff000 0x33000>,
> +			      <0x0 0x90100000 0x200000>,
> +			      <0x0 0x98a00000 0x600000>,
> +			      <0x0 0x9a000000 0xc00000>,
> +			      <0x0 0x9b000000 0x400000>,
> +			      <0x0 0x9bd00000 0x208000>,
> +			      <0x0 0x9c000000 0x20000>,
> +			      <0x0 0xa0000000 0x10000>,
> +			      <0x0 0xa0010000 0x400000>,
> +			      <0x0 0xa0510000 0x1000>,
> +			      <0x0 0xa0900000 0x2000>,
> +			      <0x0 0xa0902000 0x1000>,
> +			      <0x0 0xa0910000 0x3c000>,
> +			      <0x0 0xb0000000 0x200000>,
> +			      <0x0 0xb1000000 0x200000>,
> +			      <0x0 0xbbfff000 0x1000000>,
> +			      <0x0 0xbcfff000 0x1000>,
> +			      <0x0 0xbd430000 0x1250000>,
> +			      <0x0 0xd0000000 0x5d00000>,
> +			      <0x0 0xdc444000 0x2bbc000>,
> +			      <0x0 0xdf005000 0x1000>,
> +			      <0x0 0xdf008000 0x1000>,
> +			      <0x0 0xdf009000 0x12000>,
> +			      <0x0 0xdf01b000 0x21000>,
> +			      <0x0 0xdf03c000 0x1000>,
> +			      <0x0 0xdf03d000 0xfc3000>;
> +			no-map;
> +		};
> +	};
> +};
> +
> +&oscclk {
> +	clock-frequency = <26000000>;
> +};
> +
> +&watchdog {
> +	status = "okay";
> +};
> 
> --
> 2.54.0
> 
> 
>