Add `riscv set_prefer_sba`

This allows a user to tell OpenOCD to prefer system bus access for
memory access, which can be useful for testing, or when there really is
a difference in behavior.

Change-Id: I8c2f15b89a2ccdae568c68ee743b75a74f9ad6bd

src/target/riscv/riscv-013.c

@@ -2183,7 +2183,7 @@ static int read_memory(struct target *target, target_addr_t address,
 		uint32_t size, uint32_t count, uint8_t *buffer)
 {
 	RISCV013_INFO(info);
-	if (info->progbufsize >= 2)
+	if (info->progbufsize >= 2 && !riscv_prefer_sba)
 		return read_memory_progbuf(target, address, size, count, buffer);
 
 	if ((get_field(info->sbcs, DMI_SBCS_SBACCESS8) && size == 1) ||
@@ -2197,6 +2197,9 @@ static int read_memory(struct target *target, target_addr_t address,
 			return read_memory_bus_v1(target, address, size, count, buffer);
 	}
 
+	if (info->progbufsize >= 2)
+		return read_memory_progbuf(target, address, size, count, buffer);
+
 	LOG_ERROR("Don't know how to read memory on this target.");
 	return ERROR_FAIL;
 }
@@ -2550,8 +2553,9 @@ static int write_memory(struct target *target, target_addr_t address,
 		uint32_t size, uint32_t count, const uint8_t *buffer)
 {
 	RISCV013_INFO(info);
-	if (info->progbufsize >= 2)
+	if (info->progbufsize >= 2 && !riscv_prefer_sba)
 		return write_memory_progbuf(target, address, size, count, buffer);
+
 	if ((get_field(info->sbcs, DMI_SBCS_SBACCESS8) && size == 1) ||
 			(get_field(info->sbcs, DMI_SBCS_SBACCESS16) && size == 2) ||
 			(get_field(info->sbcs, DMI_SBCS_SBACCESS32) && size == 4) ||
@@ -2563,6 +2567,9 @@ static int write_memory(struct target *target, target_addr_t address,
 			return write_memory_bus_v1(target, address, size, count, buffer);
 	}
 
+	if (info->progbufsize >= 2)
+		return write_memory_progbuf(target, address, size, count, buffer);
+
 	LOG_ERROR("Don't know how to write memory on this target.");
 	return ERROR_FAIL;
 }

src/target/riscv/riscv.c

@@ -188,6 +188,8 @@ int riscv_reset_timeout_sec = DEFAULT_RESET_TIMEOUT_SEC;
 bool riscv_use_scratch_ram;
 uint64_t riscv_scratch_ram_address;
 
+bool riscv_prefer_sba;
+
 /* In addition to the ones in the standard spec, we'll also expose additional
  * CSRs in this list.
  * The list is either NULL, or a series of ranges (inclusive), terminated with
@@ -1227,6 +1229,16 @@ COMMAND_HANDLER(riscv_set_scratch_ram)
 	return ERROR_OK;
 }
 
+COMMAND_HANDLER(riscv_set_prefer_sba)
+{
+	if (CMD_ARGC != 1) {
+		LOG_ERROR("Command takes exactly 1 parameter");
+		return ERROR_COMMAND_SYNTAX_ERROR;
+	}
+	COMMAND_PARSE_ON_OFF(CMD_ARGV[0], riscv_prefer_sba);
+	return ERROR_OK;
+}
+
 void parse_error(const char *string, char c, unsigned position)
 {
 	char buf[position+2];
@@ -1438,6 +1450,14 @@ static const struct command_registration riscv_exec_command_handlers[] = {
 		.usage = "riscv set_scratch_ram none|[address]",
 		.help = "Set address of 16 bytes of scratch RAM the debugger can use, or 'none'."
 	},
+	{
+		.name = "set_prefer_sba",
+		.handler = riscv_set_prefer_sba,
+		.mode = COMMAND_ANY,
+		.usage = "riscv set_prefer_sba on|off",
+		.help = "When on, prefer to use System Bus Access to access memory. "
+			"When off, prefer to use the Program Buffer to access memory."
+	},
 	{
 		.name = "expose_csrs",
 		.handler = riscv_set_expose_csrs,

src/target/riscv/riscv.h

@@ -127,6 +127,8 @@ extern int riscv_reset_timeout_sec;
 extern bool riscv_use_scratch_ram;
 extern uint64_t riscv_scratch_ram_address;
 
+extern bool riscv_prefer_sba;
+
 /* Everything needs the RISC-V specific info structure, so here's a nice macro
  * that provides that. */
 static inline riscv_info_t *riscv_info(const struct target *target) __attribute__((unused));