RISC-V: use m/sscratch registers for barebox_riscv_pbl_flags

Use the dedicated scratch register for setting the pbl flags. Each mode
has it's own scratch register so we are not conflicting with M-mode
running firmware e.g. OpenSBI. Using the scratch register has two main
advantages:
 1st) It can be used in PBL and non-PBL use-case.
 2nd) It is not affected by the relocation code.

This commit prepares barebox to add support for the special cache ops
used by several T-Head CPUs.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Link: https://lore.barebox.org/20221005111214.148844-4-m.felsch@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

5 files changed, 51 insertions, 42 deletions

diff --git a/arch/riscv/boot/entry.c b/arch/riscv/boot/entry.c
index e4a5c2208d..f5a536fc78 100644
--- a/arch/riscv/boot/entry.c
+++ b/arch/riscv/boot/entry.c
@@ -25,6 +25,7 @@ void __noreturn __naked barebox_riscv_entry(unsigned long membase,
 {
 	unsigned long stack_top = riscv_mem_stack_top(membase, membase + memsize);
 	asm volatile ("move sp, %0" : : "r"(stack_top));
-	barebox_pbl_start(membase, memsize, boarddata, flags);
+	riscv_set_flags(flags);
+	barebox_pbl_start(membase, memsize, boarddata);
 }
 
diff --git a/arch/riscv/boot/entry.h b/arch/riscv/boot/entry.h
index fb4af5eae5..b3a24d2783 100644
--- a/arch/riscv/boot/entry.h
+++ b/arch/riscv/boot/entry.h
@@ -6,12 +6,10 @@
 
 void __noreturn barebox_non_pbl_start(unsigned long membase,
 				      unsigned long memsize,
-				      void *boarddata,
-				      unsigned flags);
+				      void *boarddata);
 
 void __noreturn barebox_pbl_start(unsigned long membase,
 				  unsigned long memsize,
-				  void *boarddata,
-				  unsigned flags);
+				  void *boarddata);
 
 #endif
diff --git a/arch/riscv/boot/start.c b/arch/riscv/boot/start.c
index 8b4c8bb2f0..27d9066243 100644
--- a/arch/riscv/boot/start.c
+++ b/arch/riscv/boot/start.c
@@ -27,7 +27,6 @@ static unsigned long riscv_barebox_size;
 static unsigned long riscv_endmem;
 static void *barebox_boarddata;
 static unsigned long barebox_boarddata_size;
-unsigned barebox_riscv_pbl_flags;
 
 void *barebox_riscv_boot_dtb(void)
 {
@@ -108,7 +107,7 @@ device_initcall(barebox_memory_areas_init);
  */
 __noreturn __no_sanitize_address __section(.text_entry)
 void barebox_non_pbl_start(unsigned long membase, unsigned long memsize,
-			   void *boarddata, unsigned flags)
+			   void *boarddata)
 {
 	unsigned long endmem = membase + memsize;
 	unsigned long malloc_start, malloc_end;
@@ -121,7 +120,7 @@ void barebox_non_pbl_start(unsigned long membase, unsigned long memsize,
 
 	barrier();
 
-	irq_init_vector(__riscv_mode(flags));
+	irq_init_vector(riscv_mode());
 
 	pr_debug("memory at 0x%08lx, size 0x%08lx\n", membase, memsize);
 
@@ -171,20 +170,18 @@ void barebox_non_pbl_start(unsigned long membase, unsigned long memsize,
 
 	mem_malloc_init((void *)malloc_start, (void *)malloc_end - 1);
 
-	barebox_riscv_pbl_flags = flags;
-
 	pr_debug("starting barebox...\n");
 
 	start_barebox();
 }
 
-void start(unsigned long membase, unsigned long memsize, void *boarddata, unsigned flags);
+void start(unsigned long membase, unsigned long memsize, void *boarddata);
 /*
  * First function in the uncompressed image. We get here from
  * the pbl. The stack already has been set up by the pbl.
  */
 void __no_sanitize_address __section(.text_entry) start(unsigned long membase,
-		unsigned long memsize, void *boarddata, unsigned flags)
+		unsigned long memsize, void *boarddata)
 {
-	barebox_non_pbl_start(membase, memsize, boarddata, flags);
+	barebox_non_pbl_start(membase, memsize, boarddata);
 }
diff --git a/arch/riscv/boot/uncompress.c b/arch/riscv/boot/uncompress.c
index 4ed9b4d371..ee24f81e01 100644
--- a/arch/riscv/boot/uncompress.c
+++ b/arch/riscv/boot/uncompress.c
@@ -24,16 +24,16 @@ unsigned long free_mem_ptr;
 unsigned long free_mem_end_ptr;
 
 void __noreturn barebox_pbl_start(unsigned long membase, unsigned long memsize,
-				  void *fdt, unsigned flags)
+				  void *fdt)
 {
 	uint32_t pg_len, uncompressed_len;
-	void __noreturn (*barebox)(unsigned long, unsigned long, void *, unsigned);
+	void __noreturn (*barebox)(unsigned long, unsigned long, void *);
 	unsigned long endmem = membase + memsize;
 	unsigned long barebox_base;
 	void *pg_start, *pg_end;
 	unsigned long pc = get_pc();
 
-	irq_init_vector(__riscv_mode(flags));
+	irq_init_vector(riscv_mode());
 
 	/* piggy data is not relocated, so determine the bounds now */
 	pg_start = input_data + get_runtime_offset();
@@ -72,5 +72,5 @@ void __noreturn barebox_pbl_start(unsigned long membase, unsigned long memsize,
 
 	pr_debug("jumping to uncompressed image at 0x%p. dtb=0x%p\n", barebox, fdt);
 
-	barebox(membase, memsize, fdt, flags);
+	barebox(membase, memsize, fdt);
 }
diff --git a/arch/riscv/include/asm/system.h b/arch/riscv/include/asm/system.h
index 89516f075b..f0b6bf2945 100644
--- a/arch/riscv/include/asm/system.h
+++ b/arch/riscv/include/asm/system.h
@@ -15,7 +15,39 @@ enum riscv_mode {
     RISCV_M_MODE	= 3,
 };
 
-static inline enum riscv_mode __riscv_mode(u32 flags)
+static inline void riscv_set_flags(unsigned flags)
+{
+	switch (flags & RISCV_MODE_MASK) {
+	case RISCV_S_MODE:
+		__asm__ volatile("csrw sscratch, %0" : : "r"(flags));
+		break;
+	case RISCV_M_MODE:
+		__asm__ volatile("csrw mscratch, %0" : : "r"(flags));
+		break;
+	default:
+		/* Other modes are not implemented yet */
+		break;
+	}
+}
+
+static inline u32 riscv_get_flags(void)
+{
+	u32 flags = 0;
+
+	if (IS_ENABLED(CONFIG_RISCV_S_MODE))
+		__asm__ volatile("csrr %0, sscratch" : "=r"(flags));
+
+	/*
+	 * Since we always set the scratch register on the very beginning, a
+	 * empty flags indicates that we are running in M-mode.
+	 */
+	if (!flags)
+		__asm__ volatile("csrr %0, mscratch" : "=r"(flags));
+
+	return flags;
+}
+
+static inline enum riscv_mode riscv_mode(void)
 {
 	/* allow non-LTO builds to discard code for unused modes */
 	if (!IS_ENABLED(CONFIG_RISCV_MULTI_MODE)) {
@@ -25,14 +57,14 @@ static inline enum riscv_mode __riscv_mode(u32 flags)
 			return RISCV_S_MODE;
 	}
 
-	return flags & RISCV_MODE_MASK;
+	return riscv_get_flags() & RISCV_MODE_MASK;
 }
 
-static inline long __riscv_hartid(u32 flags)
+static inline long riscv_hartid(void)
 {
 	long hartid = -1;
 
-	switch (__riscv_mode(flags)) {
+	switch (riscv_mode()) {
 	case RISCV_S_MODE:
 		__asm__ volatile("mv %0, tp\n" : "=r"(hartid) :);
 		break;
@@ -44,12 +76,12 @@ static inline long __riscv_hartid(u32 flags)
 	return hartid;
 }
 
-static inline long __riscv_vendor_id(u32 flags)
+static inline long riscv_vendor_id(void)
 {
 	struct sbiret ret;
 	long id;
 
-	switch (__riscv_mode(flags)) {
+	switch (riscv_mode()) {
 	case RISCV_M_MODE:
 		__asm__ volatile("csrr %0, mvendorid\n" : "=r"(id));
 		return id;
@@ -68,25 +100,6 @@ static inline long __riscv_vendor_id(u32 flags)
 	}
 }
 
-#ifndef __PBL__
-extern unsigned barebox_riscv_pbl_flags;
-
-static inline enum riscv_mode riscv_mode(void)
-{
-	return __riscv_mode(barebox_riscv_pbl_flags);
-}
-
-static inline long riscv_hartid(void)
-{
-	return __riscv_hartid(barebox_riscv_pbl_flags);
-}
-
-static inline long riscv_vendor_id(void)
-{
-	return __riscv_vendor_id(barebox_riscv_pbl_flags);
-}
-#endif
-
 #endif
 
 #endif