[1/2] pdbg: Rework backend detection

diff --git a/src/main.c b/src/main.c
index 883e892..8b7e2dd 100644
--- a/src/main.c
+++ b/src/main.c
@@ -405,7 +405,6 @@  static bool parse_options(int argc, char *argv[])
 		case 'b':
 			if (strcmp(optarg, "fsi") == 0) {
 				backend = FSI;
-				device_node = "p9w";
 			} else if (strcmp(optarg, "i2c") == 0) {
 				backend = I2C;
 			} else if (strcmp(optarg, "kernel") == 0) {
@@ -418,6 +417,7 @@  static bool parse_options(int argc, char *argv[])
 				backend = HOST;
 			} else {
 				fprintf(stderr, "Invalid backend '%s'\n", optarg);
+				print_backends(stderr);
 				opt_error = true;
 			}
 			break;
@@ -630,7 +630,7 @@  static int target_selection(void)
 	case KERNEL:
 		if (device_node == NULL) {
 			PR_ERROR("kernel backend requires a device type\n");
-			return -1;
+                        return -1;
 		}
 		if (!strcmp(device_node, "p8"))
 			pdbg_targets_init(&_binary_p8_kernel_dtb_o_start);
@@ -662,7 +662,9 @@  static int target_selection(void)
 		break;
 
 	default:
-		PR_ERROR("Invalid backend specified\n");
+		/* parse_options deals with parsing user input, so it should be
+		 * impossible to get here */
+		assert(0);
 		return -1;
 	}
 
@@ -797,29 +799,18 @@  int main(int argc, char *argv[])
 	optcmd_cmd_t *cmd;
 
 	backend = default_backend();
-	device_node = default_target(backend);
 
 	if (!parse_options(argc, argv))
 		return 1;
 
-	if (!backend_is_possible(backend)) {
-		fprintf(stderr, "Backend not possible\nUse: ");
-		print_backends(stderr);
-		return 1;
-	}
-
-	if (!target_is_possible(backend, device_node)) {
-		fprintf(stderr, "Target %s not possible\n",
-			device_node ? device_node : "(none)");
-		print_targets(stderr);
-		return 1;
-	}
-
 	if (optind >= argc) {
 		print_usage(basename(argv[0]));
 		return 1;
 	}
 
+	if (!device_node)
+		device_node = default_target(backend);
+
 	/* Disable unselected targets */
 	if (target_selection())
 		return 1;
diff --git a/src/options.h b/src/options.h
index 54436b6..67f15a8 100644
--- a/src/options.h
+++ b/src/options.h
@@ -20,17 +20,8 @@  enum backend default_backend(void);
 /* Print all possible backends on this platform */
 void print_backends(FILE *stream);
 
-/* Is this backend possible on this platform */
-bool backend_is_possible(enum backend backend);
-
 /* The default (perhaps only) target for this backend */
 const char *default_target(enum backend backend);
 
 /* Print all possible targets on this platform */
 void print_targets(FILE *stream);
-
-/*
- * Does this platform backend support this target,
- * there is an implied check of is_backend_possible()
- */
-bool target_is_possible(enum backend backend, const char *target);
diff --git a/src/options_arm.c b/src/options_arm.c
index 72985d3..d43e5ee 100644
--- a/src/options_arm.c
+++ b/src/options_arm.c
@@ -22,11 +22,6 @@ 
 #define AMI_BMC "/proc/ractrends/Helper/FwInfo"
 #define OPENFSI_BMC "/sys/bus/platform/devices/gpio-fsi/fsi0/"
 
-static const char witherspoon[] = "p9w";
-static const char romulus[] = "p9r";
-static const char zaius[] = "p9z";
-static const char p8[] = "p8";
-
 enum backend default_backend(void)
 {
 	int rc;
@@ -43,17 +38,7 @@  enum backend default_backend(void)
 
 void print_backends(FILE *stream)
 {
-	fprintf(stream, "Valid backends: i2c kernel fsi\n");
-}
-
-bool backend_is_possible(enum backend backend)
-{
-	if (backend == I2C)
-		return true;
-	if (backend == KERNEL && access(OPENFSI_BMC, F_OK) == 0)
-		return true;
-
-	return backend == FSI;
+	fprintf(stream, "Valid backends: i2c kernel fsi fake\n");
 }
 
 void print_targets(FILE *stream)
@@ -63,15 +48,12 @@  void print_targets(FILE *stream)
 	fprintf(stream, "fsi: p8 p9w p9r p9z\n");
 }
 
-const char *default_target(enum backend backend)
+static const char *default_fsi_target(void)
 {
 	FILE *dt_compatible;
 	char line[256];
 	char *p;
 
-	if (backend == I2C || backend == KERNEL) /* No target nessesary */
-		return NULL;
-
 	dt_compatible = fopen("/proc/device-tree/compatible", "r");
 	if (!dt_compatible)
 		return NULL;
@@ -82,33 +64,39 @@  const char *default_target(enum backend backend)
 		return NULL;
 
 	if (strstr(line, "witherspoon"))
-		return witherspoon;
+		return "p9w";
 
 	if (strstr(line, "romulus"))
-		return romulus;
+		return "p9r";
 
 	if (strstr(line, "zaius"))
-		return zaius;
+		return "p9z";
 
 	if (strstr(line, "palmetto"))
-		return p8;
+		return "p8";
 
 	return NULL;
 }
 
-bool target_is_possible(enum backend backend, const char *target)
+const char *default_target(enum backend backend)
 {
-	const char *def;
+	switch(backend) {
+	case I2C:
+		return NULL;
+		break;
 
-	if (!backend_is_possible(backend))
-		return false;
+	case KERNEL:
+		return NULL;
+		break;
 
-	if (backend == I2C || backend == KERNEL) /* No target is nessesary */
-		return true;
+	case FSI:
+		return default_fsi_target();
+		break;
 
-	def = default_target(backend);
-	if (!def || !target)
-		return false;
+	default:
+		return NULL;
+		break;
+	}
 
-	return strcmp(def, target) == 0;
+	return NULL;
 }
diff --git a/src/options_def.c b/src/options_def.c
index d6b96ce..4092cea 100644
--- a/src/options_def.c
+++ b/src/options_def.c
@@ -22,11 +22,6 @@  enum backend default_backend(void)
 	return FAKE;
 }
 
-bool backend_is_possible(enum backend backend)
-{
-	return backend == FAKE;
-}
-
 void print_backends(FILE *stream)
 {
 	fprintf(stream, "Valid backends: fake\n");
@@ -42,9 +37,3 @@  void print_targets(FILE *stream)
 {
 	fprintf(stream, "fake: No target is necessary\n");
 }
-
-/* Theres no device for FAKE backend */
-bool target_is_possible(enum backend backend, const char *target)
-{
-	return target == NULL;
-}
diff --git a/src/options_ppc.c b/src/options_ppc.c
index 3478799..62eb7b0 100644
--- a/src/options_ppc.c
+++ b/src/options_ppc.c
@@ -26,15 +26,9 @@  enum backend default_backend(void)
 	return HOST;
 }
 
-bool backend_is_possible(enum backend backend)
-{
-	/* TODO */
-	return backend == HOST;
-}
-
 void print_backends(FILE *stream)
 {
-	fprintf(stream, "Valid backends: host\n");
+	fprintf(stream, "Valid backends: host fake\n");
 }
 
 const char *default_target(enum backend backend)
@@ -76,17 +70,3 @@  void print_targets(FILE *stream)
 {
 	fprintf(stream, "host: p8 p9\n");
 }
-
-bool target_is_possible(enum backend backend, const char *target)
-{
-	const char *def;
-
-	if (!backend_is_possible(backend))
-		return false;
-
-	def = default_target(backend);
-	if (!def || !target)
-		return false;
-
-	return strcmp(def, target) == 0;
-}