firmware: Add separate dummy payload for FW_PAYLOAD

Currently, the default payload for FW_PAYLOAD is embedded
fw_payload.S itself. This means people have to hack fw_payload.S
if they want to have some temporary S-mode test code.

This patch adds a separate dummy payload for FW_PAYLOAD which
can be easily hacked for some S-mode testing.

Signed-off-by: Anup Patel <anup.patel@wdc.com>

firmware/payloads/dummy.elf.ldS

@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2018 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *   Anup Patel <anup.patel@wdc.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+OUTPUT_ARCH(riscv)
+ENTRY(_start)
+
+SECTIONS
+{
+	. = FW_TEXT_START + FW_PAYLOAD_OFFSET;
+
+	PROVIDE(_payload_start = .);
+
+	. = ALIGN(0x1000); /* Need this to create proper sections */
+
+	/* Beginning of the code section */
+
+	.text :
+	{
+		PROVIDE(_text_start = .);
+		*(.entry)
+		*(.text)
+		. = ALIGN(8);
+		PROVIDE(_text_end = .);
+	}
+
+	. = ALIGN(0x1000); /* Ensure next section is page aligned */
+
+	/* End of the code sections */
+
+	/* Beginning of the read-only data sections */
+
+	. = ALIGN(0x1000); /* Ensure next section is page aligned */
+
+	.rodata :
+	{
+		PROVIDE(_rodata_start = .);
+		*(.rodata .rodata.*)
+		. = ALIGN(8);
+		PROVIDE(_rodata_end = .);
+	}
+
+	/* End of the read-only data sections */
+
+	/* Beginning of the read-write data sections */
+
+	. = ALIGN(0x1000); /* Ensure next section is page aligned */
+
+	.data :
+	{
+		PROVIDE(_data_start = .);
+
+		*(.data)
+		*(.data.*)
+		*(.readmostly.data)
+		*(*.data)
+		. = ALIGN(8);
+
+		PROVIDE(_data_end = .);
+	}
+
+	. = ALIGN(0x1000); /* Ensure next section is page aligned */
+
+	.bss :
+	{
+		PROVIDE(_bss_start = .);
+		*(.bss)
+		*(.bss.*)
+		. = ALIGN(8);
+		PROVIDE(_bss_end = .);
+	}
+
+	/* End of the read-write data sections */
+
+	. = ALIGN(0x1000); /* Need this to create proper sections */
+
+	PROVIDE(_payload_end = .);
+}

firmware/payloads/dummy_head.S

@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2018 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *   Anup Patel <anup.patel@wdc.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#define __ASM_STR(x)	x
+
+#if __riscv_xlen == 64
+#define __REG_SEL(a, b)		__ASM_STR(a)
+#define RISCV_PTR		.dword
+#elif __riscv_xlen == 32
+#define __REG_SEL(a, b)		__ASM_STR(b)
+#define RISCV_PTR		.word
+#else
+#error "Unexpected __riscv_xlen"
+#endif
+
+#define REG_L		__REG_SEL(ld, lw)
+#define REG_S		__REG_SEL(sd, sw)
+
+	.align 3
+	.section .entry, "ax", %progbits
+	.globl _start
+_start:
+	/* Pick one hart to run the main boot sequence */
+	la	a3, _hart_lottery
+	li	a2, 1
+	amoadd.w a3, a2, (a3)
+	bnez	a3, _start_hang
+
+	/* Save a0 and a1 */
+	la	a3, _boot_a0
+	REG_S	a0, 0(a3)
+	la	a3, _boot_a1
+	REG_S	a1, 0(a3)
+
+	/* Zero-out BSS */
+	la	a4, _bss_start
+	la	a5, _bss_end
+_bss_zero:
+	REG_S	zero, (a4)
+	add	a4, a4, __SIZEOF_POINTER__
+	blt	a4, a5, _bss_zero
+
+_start_warm:
+	/* Disable and clear all interrupts */
+	csrw	sie, zero
+	csrw	sip, zero
+
+	/* Setup exception vectors */
+	la	a3, _start_hang
+	csrw	stvec, a3
+
+	/* Setup stack */
+	la	a3, _payload_end
+	li	a4, 0x2000
+	add	sp, a3, a4
+
+	/* Jump to C main */
+	la	a3, _boot_a0
+	REG_L	a0, 0(a3)
+	la	a3, _boot_a1
+	REG_L	a1, 0(a3)
+	call	dummy_main
+
+	/* We don't expect to reach here hence just hang */
+	j	_start_hang
+
+	.align 3
+	.section .entry, "ax", %progbits
+	.globl _start_hang
+_start_hang:
+	wfi
+	j	_start_hang
+
+	.align	3
+	.section .entry, "ax", %progbits
+_hart_lottery:
+	RISCV_PTR	0
+_boot_a0:
+	RISCV_PTR	0
+_boot_a1:
+	RISCV_PTR	0

firmware/payloads/dummy_main.c

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2018 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *   Anup Patel <anup.patel@wdc.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <sbi/sbi_ecall_interface.h>
+
+#define wfi()						\
+do {							\
+	__asm__ __volatile__ ("wfi" ::: "memory");	\
+} while (0)
+
+static void sbi_puts(const char *str)
+{
+	while (*str) {
+		SBI_ECALL_1(SBI_ECALL_CONSOLE_PUTCHAR, *str);
+		str++;
+	}
+}
+
+void dummy_main(unsigned long a0, unsigned long a1)
+{
+	sbi_puts("\nDummy Payload\n");
+
+	while (1)
+		wfi();
+}

firmware/payloads/objects.mk

@@ -0,0 +1,19 @@
+#
+# Copyright (c) 2018 Western Digital Corporation or its affiliates.
+#
+# Authors:
+#   Anup Patel <anup.patel@wdc.com>
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+firmware-bins-$(FW_PAYLOAD) += payloads/dummy.bin
+
+dummy-y += dummy_head.o
+dummy-y += dummy_main.o
+
+%/dummy.o: $(foreach obj,$(dummy-y),%/$(obj))
+	$(call merge_objs,$@,$^)
+
+%/dummy.dep: $(foreach dep,$(dummy-y:.o=.dep),%/$(dep))
+	$(call merge_deps,$@,$^)