arch/riscv: Pass cbmem_top to ramstage via calling argument

Tested on the Qemu-Virt target both 32 and 64 bit.

Change-Id: I5c74cd5d3ee292931c5bbd2e4075f88381429f72
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36558
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/arch/riscv/index.md

@@ -19,6 +19,9 @@ On entry to a stage or payload (including SELF payloads),
 * all harts are running.
 * A0 is the hart ID.
 * A1 is the pointer to the Flattened Device Tree (FDT).
+* A2 contains the additional program calling argument:
+  - cbmem_top for ramstage
+  - the address of the payload for opensbi
 
 ## Additional payload handoff requirements
 The location of cbmem should be placed in a node in the FDT.

src/arch/riscv/Kconfig

@@ -90,6 +90,7 @@ config ARCH_ROMSTAGE_RISCV
 config ARCH_RAMSTAGE_RISCV
 	bool
 	default n
+	select RAMSTAGE_CBMEM_TOP_ARG
 
 config RISCV_USE_ARCH_TIMER
 	bool

src/arch/riscv/boot.c

@@ -36,7 +36,7 @@ struct arch_prog_run_args {
 
 static void do_arch_prog_run(struct arch_prog_run_args *args)
 {
-	int hart_id;
+	int hart_id = HLS()->hart_id;
 	struct prog *prog = args->prog;
 	void *fdt = HLS()->fdt;
 
@@ -49,11 +49,8 @@ static void do_arch_prog_run(struct arch_prog_run_args *args)
 		else
 			run_payload(prog, fdt, RISCV_PAYLOAD_MODE_S);
 	} else {
-		void (*doit)(int hart_id, void *fdt) = prog_entry(prog);
-
-		hart_id = HLS()->hart_id;
-
-		doit(hart_id, fdt);
+		void (*doit)(int hart_id, void *fdt, void *arg) = prog_entry(prog);
+		doit(hart_id, fdt, prog_entry_arg(prog));
 	}
 
 	die("Failed to run stage");

src/arch/riscv/ramstage.S

@@ -20,6 +20,13 @@
 .section ".text._start", "ax", %progbits
 .globl _start
 _start:
+	/* cbmem_top is passed via a2 */
+	la   t0, _cbmem_top_ptr
+#if __riscv_xlen == 32
+	sw   a2, (t0)
+#elif __riscv_xlen == 64
+	sd   a2, (t0)
+#endif
 	# initialize stack point for each hart
 	# and the stack must be page-aligned.
 	# 0xDEADBEEF used to check stack overflow