Add support for amlogic s4 (S805X2/S905W2/S905Y4) SoCs. These are very
similar to other recent SoCs, with the exception of a workaround for
some BL2 (mis)behavior. Memory for ATF/TEE is expected to be reserved in
the board devicetree, so we don't reserve it in board-s4.c.

Signed-off-by: Sean Anderson <[email protected]>
---

Changes in v2:
- Add S4 to meson board info
- Add DEBUG_UART defaults
- Extend initial padding to 4096 to match what Amlogic does

 arch/arm/include/asm/arch-meson/boot0.h | 12 ++++++
 arch/arm/mach-meson/Kconfig             |  7 ++++
 arch/arm/mach-meson/Makefile            |  1 +
 arch/arm/mach-meson/board-info.c        |  2 +
 arch/arm/mach-meson/board-s4.c          | 50 +++++++++++++++++++++++++
 drivers/serial/Kconfig                  |  2 +
 6 files changed, 74 insertions(+)
 create mode 100644 arch/arm/include/asm/arch-meson/boot0.h
 create mode 100644 arch/arm/mach-meson/board-s4.c

diff --git a/arch/arm/include/asm/arch-meson/boot0.h 
b/arch/arm/include/asm/arch-meson/boot0.h
new file mode 100644
index 00000000000..d098786e5f1
--- /dev/null
+++ b/arch/arm/include/asm/arch-meson/boot0.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2026 Brivo Systems LLC
+ */
+b reset
+/*
+ * BL2 copies some keys to the start of DRAM, clobbering anything in the first
+ * 4k aside from the initial instruction. I measured the actual data clobbered
+ * as 1076 bytes, but I suspect the amount depends on the configuration, so
+ * just go with what amlogic does.
+ */
+.skip 4096
diff --git a/arch/arm/mach-meson/Kconfig b/arch/arm/mach-meson/Kconfig
index c687ef822a2..91d1e8342e0 100644
--- a/arch/arm/mach-meson/Kconfig
+++ b/arch/arm/mach-meson/Kconfig
@@ -67,6 +67,13 @@ config MESON_A1
        help
          Select this if your SoC is an A113L
 
+config MESON_S4
+       bool "S4"
+       select MESON64_COMMON
+       select ENABLE_ARM_SOC_BOOT0_HOOK
+       help
+         Select this if your SoC is an S905Y4/S905W2/S805X2
+
 endchoice
 
 config SYS_SOC
diff --git a/arch/arm/mach-meson/Makefile b/arch/arm/mach-meson/Makefile
index 08a24d4b24f..2157c35c2d5 100644
--- a/arch/arm/mach-meson/Makefile
+++ b/arch/arm/mach-meson/Makefile
@@ -17,3 +17,4 @@ endif
 obj-$(CONFIG_MESON_AXG) += board-axg.o
 obj-$(CONFIG_MESON_G12A) += board-g12a.o
 obj-$(CONFIG_MESON_A1) += board-a1.o
+obj-$(CONFIG_MESON_S4) += board-s4.o
diff --git a/arch/arm/mach-meson/board-info.c b/arch/arm/mach-meson/board-info.c
index d3807dc787d..379f6a42c22 100644
--- a/arch/arm/mach-meson/board-info.c
+++ b/arch/arm/mach-meson/board-info.c
@@ -40,6 +40,7 @@ static const struct meson_gx_soc_id {
        { "G12B",   0x29 },
        { "SM1",    0x2b },
        { "A1",     0x2c },
+       { "S4",     0x37 },
 };
 
 static const struct meson_gx_package_id {
@@ -73,6 +74,7 @@ static const struct meson_gx_package_id {
        { "S905X3", 0x2b, 0x10, 0x3f },
        { "S905D3", 0x2b, 0x30, 0x3f },
        { "A113L", 0x2c, 0x0, 0xf8 },
+       { "S905Y4", 0x37, 0x03, 0xff },
 };
 
 DECLARE_GLOBAL_DATA_PTR;
diff --git a/arch/arm/mach-meson/board-s4.c b/arch/arm/mach-meson/board-s4.c
new file mode 100644
index 00000000000..7d0bea9924f
--- /dev/null
+++ b/arch/arm/mach-meson/board-s4.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * (C) Copyright 2023 SberDevices, Inc.
+ */
+
+#include <asm/armv8/mmu.h>
+#include <asm/io.h>
+#include <linux/compiler.h>
+#include <linux/errno.h>
+
+void meson_init_reserved_memory(__maybe_unused void *fdt)
+{
+}
+
+int meson_get_boot_device(void)
+{
+       return -ENOSYS;
+}
+
+static struct mm_region s4_mem_map[] = {
+       {
+               .virt = 0x00000000UL,
+               .phys = 0x00000000UL,
+               .size = 0x80000000UL,
+               .attrs = PTE_BLOCK_MEMTYPE(MT_NORMAL) |
+                       PTE_BLOCK_INNER_SHARE
+       }, {
+               .virt = 0x80000000UL,
+               .phys = 0x80000000UL,
+               .size = 0x7FE00000UL,
+               .attrs = PTE_BLOCK_MEMTYPE(MT_DEVICE_NGNRNE) |
+                       PTE_BLOCK_NON_SHARE |
+                       PTE_BLOCK_PXN | PTE_BLOCK_UXN
+       }, {
+               /*
+                * This mem region contains in/out shared memory with bl31,
+                * hence it's marked as NORMAL memory type
+                */
+               .virt = 0xFFE00000UL,
+               .phys = 0xFFE00000UL,
+               .size = 0x00200000UL,
+               .attrs = PTE_BLOCK_MEMTYPE(MT_NORMAL) |
+                       PTE_BLOCK_INNER_SHARE
+       }, {
+               /* List terminator */
+               0,
+       }
+};
+
+struct mm_region *mem_map = s4_mem_map;
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index ffc58d663ff..909e5e4c5f5 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -537,6 +537,7 @@ config DEBUG_UART_BASE
        default 0xe0000000 if DEBUG_UART_ZYNQ && ARCH_ZYNQ
        default 0xff000000 if DEBUG_UART_PL011 && ARCH_VERSAL
        default 0xf1920000 if DEBUG_UART_PL011 && (ARCH_VERSAL_NET || 
ARCH_VERSAL2)
+       default 0xfe07a000 if DEBUG_UART_MESON && MESON_S4
        help
          This is the base address of your UART for memory-mapped UARTs.
 
@@ -573,6 +574,7 @@ config DEBUG_UART_CLOCK
        default 100000000 if DEBUG_UART_ZYNQ && ARCH_ZYNQMP
        default 50000000 if DEBUG_UART_ZYNQ && ARCH_ZYNQ
        default 100000000 if DEBUG_UART_PL011 && (ARCH_VERSAL || 
ARCH_VERSAL_NET || ARCH_VERSAL2)
+       default 24000000 if DEBUG_UART_MESON && MESON_S4
        help
          The UART input clock determines the speed of the internal UART
          circuitry. The baud rate is derived from this by dividing the input
-- 
2.53.0

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