riscv: Introduce CONFIG_XIP to support booting from flash

When U-Boot boots from flash, during the boot process,
hart_lottery and available_harts_lock variable addresses
point to flash which is not writable. This causes boot
failures on AE350. Introduce a config option CONFIG_XIP
to support such configuration.

Signed-off-by: Rick Chen <rick@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/riscv/Kconfig

@@ -162,6 +162,13 @@ config SBI_IPI
 	default y if RISCV_SMODE
 	depends on SMP
 
+config XIP
+	bool "XIP mode"
+	help
+	  XIP (eXecute In Place) is a method for executing code directly
+	  from a NOR flash memory without copying the code to ram.
+	  Say yes here if U-Boot boots from flash directly.
+
 config STACK_SIZE_SHIFT
 	int
 	default 13

arch/riscv/cpu/cpu.c

@@ -16,6 +16,7 @@
  * before the bss section is available.
  */
 phys_addr_t prior_stage_fdt_address __attribute__((section(".data")));
+#ifndef CONFIG_XIP
 u32 hart_lottery __attribute__((section(".data"))) = 0;
 
 /*
@@ -23,6 +24,7 @@ u32 hart_lottery __attribute__((section(".data"))) = 0;
  * finished initialization of global data.
  */
 u32 available_harts_lock = 1;
+#endif
 
 static inline bool supports_extension(char ext)
 {

arch/riscv/cpu/start.S

@@ -98,6 +98,7 @@ call_board_init_f_0:
 	mv	sp, a0
 #endif
 
+#ifndef CONFIG_XIP
 	/*
 	 * Pick hart to initialize global data and run U-Boot. The other harts
 	 * wait for initialization to complete.
@@ -106,6 +107,9 @@ call_board_init_f_0:
 	li	s2, 1
 	amoswap.w s2, t1, 0(t0)
 	bnez	s2, wait_for_gd_init
+#else
+	bnez	tp, secondary_hart_loop
+#endif
 
 	la	t0, prior_stage_fdt_address
 	SREG	s1, 0(t0)
@@ -115,6 +119,7 @@ call_board_init_f_0:
 	/* save the boot hart id to global_data */
 	SREG	tp, GD_BOOT_HART(gp)
 
+#ifndef CONFIG_XIP
 	la	t0, available_harts_lock
 	fence	rw, w
 	amoswap.w zero, zero, 0(t0)
@@ -141,6 +146,7 @@ wait_for_gd_init:
 	 * secondary_hart_loop.
 	 */
 	bnez	s2, secondary_hart_loop
+#endif
 
 	/* Enable cache */
 	jal	icache_enable

arch/riscv/include/asm/global_data.h

@@ -27,7 +27,9 @@ struct arch_global_data {
 #ifdef CONFIG_SMP
 	struct ipi_data ipi[CONFIG_NR_CPUS];
 #endif
+#ifndef CONFIG_XIP
 	ulong available_harts;
+#endif
 };
 
 #include <asm-generic/global_data.h>

arch/riscv/lib/asm-offsets.c

@@ -14,7 +14,9 @@
 int main(void)
 {
 	DEFINE(GD_BOOT_HART, offsetof(gd_t, arch.boot_hart));
+#ifndef CONFIG_XIP
 	DEFINE(GD_AVAILABLE_HARTS, offsetof(gd_t, arch.available_harts));
+#endif
 
 	return 0;
 }

arch/riscv/lib/smp.c

@@ -63,9 +63,11 @@ static int send_ipi_many(struct ipi_data *ipi)
 			continue;
 		}
 
+#ifndef CONFIG_XIP
 		/* skip if hart is not available */
 		if (!(gd->arch.available_harts & (1 << reg)))
 			continue;
+#endif
 
 		gd->arch.ipi[reg].addr = ipi->addr;
 		gd->arch.ipi[reg].arg0 = ipi->arg0;