RISCV: Clean up the common architectural code

This version of coreboot successfully starts a Harvey (Plan 9) kernel as a payload,
entering main() with no supporting assembly code for startup. The Harvey port
is not complete so it just panics but ... it gets started.

We provide a standard payload function that takes a pointer argument
and makes the jump from machine to supervisor mode;
the days of kernels running in machine mode are over.

We do some small tweaks to the virtual memory code. We temporarily
disable two functions that won't work on some targets as register
numbers changed between 1.7 and 1.9. Once lowrisc catches up
we'll reenable them.

We add the PAGETABLES to the memlayout.ld and use _pagetables in the virtual
memory setup code.

We now use the _stack and _estack from memlayout so we know where things are.
As time goes on maybe we can kill all the magic numbers.

Change-Id: I6caadfa9627fa35e31580492be01d4af908d31d9
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: https://review.coreboot.org/17058
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
diff --git a/src/arch/riscv/Makefile.inc b/src/arch/riscv/Makefile.inc
index 4bab459..cf6ce99 100644
--- a/src/arch/riscv/Makefile.inc
+++ b/src/arch/riscv/Makefile.inc
@@ -96,6 +96,7 @@
 ramstage-y += boot.c
 ramstage-y += tables.c
 ramstage-y += sbi.S
+ramstage-y += payload.S
 ramstage-y += \
 	$(top)/src/lib/memchr.c \
 	$(top)/src/lib/memcmp.c \
diff --git a/src/arch/riscv/boot.c b/src/arch/riscv/boot.c
index 7435490..ff1844e 100644
--- a/src/arch/riscv/boot.c
+++ b/src/arch/riscv/boot.c
@@ -17,13 +17,17 @@
 #include <vm.h>
 #include <arch/encoding.h>
 #include <rules.h>
+#include <console/console.h>
 
 void arch_prog_run(struct prog *prog)
 {
 	void (*doit)(void *) = prog_entry(prog);
+	void riscvpayload(void *);
 
 	if (ENV_RAMSTAGE && prog_type(prog) == PROG_PAYLOAD) {
 		initVirtualMemory();
+		printk(BIOS_SPEW, "OK, let's go\n");
+		riscvpayload(doit);
 	}
 
 	doit(prog_entry_arg(prog));
diff --git a/src/arch/riscv/bootblock.S b/src/arch/riscv/bootblock.S
index 514511e..63df92b 100644
--- a/src/arch/riscv/bootblock.S
+++ b/src/arch/riscv/bootblock.S
@@ -19,13 +19,16 @@
 
 .section ".text._start", "ax", %progbits
 
+.globl _stack
+.global _estack
 .globl _start
 _start:
 
-#define STACK_START 0x80800000 /* 2GiB + 8MiB */
-#define STACK_SIZE  0x0000fff0
 
-	li sp, STACK_START + STACK_SIZE
+
+	# N.B. This only works on low 4G of the address space
+	# and the stack must be page-aligned.
+	la sp, _estack
 
 	# make room for HLS and initialize it
 	addi sp, sp, -64 // MENTRY_FRAME_SIZE
@@ -33,7 +36,7 @@
 	call hls_init
 
 	# poison the stack
-	li t1, STACK_START
+	la t1, _stack
 	li t0, 0xdeadbeef
 	sd t0, 0(t1)
 
diff --git a/src/arch/riscv/include/arch/memlayout.h b/src/arch/riscv/include/arch/memlayout.h
index 4d2af59..5d01141 100644
--- a/src/arch/riscv/include/arch/memlayout.h
+++ b/src/arch/riscv/include/arch/memlayout.h
@@ -18,8 +18,8 @@
 #ifndef __ARCH_MEMLAYOUT_H
 #define __ARCH_MEMLAYOUT_H
 
-/* TODO: Double-check that that's the correct alignment for our ABI. */
-#define STACK(addr, size) REGION(stack, addr, size, 8)
+#define STACK(addr, size) REGION(stack, addr, size, 4096)
+#define PAGETABLES(addr, size) REGION(pagetables, addr, size, 4096)
 
 /* TODO: Need to add DMA_COHERENT region like on ARM? */
 
diff --git a/src/arch/riscv/include/vm.h b/src/arch/riscv/include/vm.h
index bee2ed4..c3de47a 100644
--- a/src/arch/riscv/include/vm.h
+++ b/src/arch/riscv/include/vm.h
@@ -37,16 +37,6 @@
 #define VA_BITS 39
 #define MEGAPAGE_SIZE (SUPERPAGE_SIZE << RISCV_PGLEVEL_BITS)
 
-#define PROT_READ 1
-#define PROT_WRITE 2
-#define PROT_EXEC 4
-
-#define MAP_PRIVATE 0x2
-#define MAP_FIXED 0x10
-#define MAP_ANONYMOUS 0x20
-#define MAP_POPULATE 0x8000
-#define MREMAP_FIXED 0x2
-
 #define EXTRACT_FIELD(val, which) (((val) & (which)) / ((which) & ~((which)-1)))
 #define INSERT_FIELD(val, which, fieldval) (((val) & ~(which)) | ((fieldval) * ((which) & ~((which)-1))))
 
@@ -66,7 +56,8 @@
 
 void print_page_table(void);
 
-void init_vm(uintptr_t virtMemStart, uintptr_t physMemStart, uintptr_t pageTableStart);
+void init_vm(uintptr_t virtMemStart, uintptr_t physMemStart,
+		pte_t *pageTableStart);
 void mstatus_init(void); // need to setup mstatus so we know we have virtual memory
 
 void flush_tlb(void);
diff --git a/src/arch/riscv/payload.S b/src/arch/riscv/payload.S
new file mode 100644
index 0000000..3261a80
--- /dev/null
+++ b/src/arch/riscv/payload.S
@@ -0,0 +1,28 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+	.global riscvpayload
+riscvpayload:
+	/* Jump to a0 in S-mode */
+	mv t0,a0
+	csrw mepc, t0
+	csrr t0, mstatus
+	li t1, ~(3<<11)
+	and t0, t0, t1
+	li t2,  (1<<11)
+	or t0, t0, t2
+	csrw mstatus, t0
+
+	// We're still in toolchain no mans land.
+	.word 0x30200073
+	//mret
diff --git a/src/arch/riscv/virtual_memory.c b/src/arch/riscv/virtual_memory.c
index be8b488..999d73c 100644
--- a/src/arch/riscv/virtual_memory.c
+++ b/src/arch/riscv/virtual_memory.c
@@ -21,6 +21,7 @@
 #include <console/console.h>
 #include <stdint.h>
 #include <vm.h>
+#include <symbols.h>
 
 pte_t* root_page_table;
 
@@ -94,7 +95,7 @@
 
 /* Print the page table structures to the console */
 void print_page_table(void) {
-	print_page_table_at(root_page_table, 0, 0);
+	print_page_table_at((void *)(read_csr(sptbr) << RISCV_PGSHIFT), 0, 0);
 }
 
 void flush_tlb(void)
@@ -115,17 +116,17 @@
 pte_t pte_create(uintptr_t ppn, int prot, int user)
 {
 	pte_t pte = (ppn << PTE_PPN_SHIFT) | PTE_R | PTE_V;
-	if (prot & PROT_WRITE)
+	if (prot & PTE_W)
 		pte |= PTE_W;
-	if (prot & PROT_EXEC)
+	if (prot & PTE_X)
 		pte |= PTE_X;
 	if (user)
 		pte |= PTE_U;
 	return pte;
 }
 
-void init_vm(uintptr_t virtMemStart, uintptr_t physMemStart, uintptr_t pageTableStart) {
-	pte_t* sbi_pt = (pte_t*) pageTableStart;
+void init_vm(uintptr_t virtMemStart, uintptr_t physMemStart, pte_t *sbi_pt)
+{
 	memset(sbi_pt, 0, RISCV_PGSIZE);
 	// need to leave room for sbi page
 	uintptr_t memorySize = 0x7F000000; // 0xFFF... - 0xFFFFFFFF81000000 - RISCV_PGSIZE
@@ -147,21 +148,32 @@
 		int l2_shift = RISCV_PGLEVEL_BITS + RISCV_PGSHIFT;
 		size_t l2_idx = (virtMemStart >> l2_shift) & ((1 << RISCV_PGLEVEL_BITS)-1);
 		l2_idx += ((vaddr - virtMemStart) >> l2_shift);
-		middle_pt[l2_idx] = pte_create(paddr >> RISCV_PGSHIFT, PROT_READ|PROT_WRITE|PROT_EXEC, 0);
+		middle_pt[l2_idx] = pte_create(paddr >> RISCV_PGSHIFT,
+					       PTE_U|PTE_R|PTE_W|PTE_X, 0);
 	}
 
 	// map SBI at top of vaddr space
-	uintptr_t num_sbi_pages = 1; // only need to map a single page for sbi interface
+	// only need to map a single page for sbi interface
+	uintptr_t num_sbi_pages = 1;
 	uintptr_t sbiStartAddress = (uintptr_t) &sbi_page;
 	uintptr_t sbiAddr = sbiStartAddress;
 	for (uintptr_t i = 0; i < num_sbi_pages; i++) {
 		uintptr_t idx = (1 << RISCV_PGLEVEL_BITS) - num_sbi_pages + i;
-		sbi_pt[idx] = pte_create(sbiAddr >> RISCV_PGSHIFT, PROT_READ|PROT_EXEC, 0);
+		sbi_pt[idx] = pte_create(sbiAddr >> RISCV_PGSHIFT,
+					 PTE_R|PTE_X, 0);
 		sbiAddr += RISCV_PGSIZE;
 	}
 	pte_t* sbi_pte = middle_pt + ((num_middle_pts << RISCV_PGLEVEL_BITS)-1);
 	*sbi_pte = ptd_create((uintptr_t)sbi_pt >> RISCV_PGSHIFT);
 
+	// IO space.
+	root_pt[0] = pte_create(0, PTE_W|PTE_R, 0);
+	root_pt[1] = pte_create(0x40000000>>RISCV_PGSHIFT,
+				PTE_W|PTE_R, 0);
+
+	// Start of RAM
+	root_pt[2] = pte_create(0x80000000>>RISCV_PGSHIFT,
+				PTE_W|PTE_R, 0);
 	mb();
 	root_page_table = root_pt;
 	uintptr_t ptbr = ((uintptr_t) root_pt) >> RISCV_PGSHIFT;
@@ -185,12 +197,13 @@
 		printk(BIOS_DEBUG, "-----------------------------\n");
 	}
 
+	// TODO: Figure out how to grab this from cbfs
 	printk(BIOS_DEBUG, "Initializing virtual memory...\n");
-	uintptr_t physicalStart = 0x90000000; // TODO: Figure out how to grab this from cbfs
-	uintptr_t virtualStart = 0xffffffff80000000;
-	uintptr_t pageTableStart = 0x91400000;
-	init_vm(virtualStart, physicalStart, pageTableStart);
+	uintptr_t physicalStart = 0x81000000;
+	uintptr_t virtualStart = 0xffffffff81000000;
+	init_vm(virtualStart, physicalStart, (pte_t *)_pagetables);
 	mb();
+	flush_tlb();
 
 #if IS_ENABLED(CONFIG_DEBUG_PRINT_PAGE_TABLES)
 	printk(BIOS_DEBUG, "Finished initializing virtual memory, starting walk...\n");
@@ -220,7 +233,12 @@
 			| (1 << CAUSE_USER_ECALL)
 	);
 
+
 	/* Enable all user/supervisor-mode counters */
-	write_csr(mscounteren, 0b111);
-	write_csr(mucounteren, 0b111);
+	/* We'll turn these on once lowrisc gets their bitstream up to
+	 * 1.9. Right now there's no agreement on the values for these
+	 * architectural registers.
+	 */
+	//write_csr(mscounteren, 0b111);
+	//write_csr(mucounteren, 0b111);
 }
diff --git a/src/include/symbols.h b/src/include/symbols.h
index d7cb35c..ea44293 100644
--- a/src/include/symbols.h
+++ b/src/include/symbols.h
@@ -41,6 +41,10 @@
 extern u8 _estack[];
 #define _stack_size (_estack - _stack)
 
+extern u8 _pagetables[];
+extern u8 _epagetables[];
+#define _pagetables_size (_epagetables - _pagetables)
+
 extern u8 _preram_cbfs_cache[];
 extern u8 _epreram_cbfs_cache[];
 #define _preram_cbfs_cache_size (_epreram_cbfs_cache - _preram_cbfs_cache)
diff --git a/src/mainboard/emulation/qemu-riscv/memlayout.ld b/src/mainboard/emulation/qemu-riscv/memlayout.ld
index 615d1f2..8cc6d41 100644
--- a/src/mainboard/emulation/qemu-riscv/memlayout.ld
+++ b/src/mainboard/emulation/qemu-riscv/memlayout.ld
@@ -24,5 +24,6 @@
 	ROMSTAGE(0x20000, 128K)
 	STACK(0x40000, 0x3ff00)
 	PRERAM_CBMEM_CONSOLE(0x80000, 8K)
+	PAGETABLES(0x80000+8K, 60K)
 	RAMSTAGE(0x100000, 16M)
 }
diff --git a/src/mainboard/emulation/spike-riscv/memlayout.ld b/src/mainboard/emulation/spike-riscv/memlayout.ld
index 8d35a64..8596723 100644
--- a/src/mainboard/emulation/spike-riscv/memlayout.ld
+++ b/src/mainboard/emulation/spike-riscv/memlayout.ld
@@ -23,7 +23,8 @@
 {
 	DRAM_START(START)
 	BOOTBLOCK(START, 64K)
-	STACK(START + 8M, 64K)
+	STACK(START + 8M, 4K)
+	PAGETABLES(START + 8M + 4K, 60K)
 	ROMSTAGE(START + 8M + 64K, 128K)
 	PRERAM_CBMEM_CONSOLE(START + 8M + 192k, 8K)
 	RAMSTAGE(START + 8M + 200K, 256K)