spl: Provide more information on boot failure

If SPL fails to boot, try to provide an error code to indicate what is
wrong. For example, if a uclass is missing, this can return -EPFNOSUPPORT
(-96) which provides useful information.

Add a helper for accessing the image-loader name so we can drop the use
of #ifdefs in this code.

Put this feature behind a CONFIG_SHOW_ERRORS option to avoid increasing
the code size.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/spl/Kconfig

@@ -91,6 +91,16 @@ config SPL_SYS_REPORT_STACK_F_USAGE
 	  occurrence of non 0xaa bytes.
 	  This default implementation works for stacks growing down only.
 
+config SPL_SHOW_ERRORS
+	bool "Show more information when something goes wrong"
+	help
+	  This enabled more verbose error messages and checking when something
+	  goes wrong in SPL. For example, it shows the error code when U-Boot
+	  cannot be located. This can help to diagnose the problem and figure
+	  out a fix, particularly during development.
+
+	  This adds a small amount to SPL code size, perhaps 100 bytes.
+
 menu "PowerPC and LayerScape SPL Boot options"
 
 config SPL_NAND_BOOT

common/spl/spl.c

@@ -593,32 +593,42 @@ static int spl_load_image(struct spl_image_info *spl_image,
  * @spl_image: Place to put the image details if successful
  * @spl_boot_list: List of boot devices to try
  * @count: Number of elements in spl_boot_list
- * @return 0 if OK, -ve on error
+ * @return 0 if OK, -ENODEV if there were no boot devices
+ *	if CONFIG_SHOW_ERRORS is enabled, returns -ENXIO if there were
+ *	devices but none worked
  */
 static int boot_from_devices(struct spl_image_info *spl_image,
 			     u32 spl_boot_list[], int count)
 {
+	int ret = -ENODEV;
 	int i;
 
 	for (i = 0; i < count && spl_boot_list[i] != BOOT_DEVICE_NONE; i++) {
 		struct spl_image_loader *loader;
+		int bootdev = spl_boot_list[i];
 
-		loader = spl_ll_find_loader(spl_boot_list[i]);
+		if (CONFIG_IS_ENABLED(SHOW_ERRORS))
-#if defined(CONFIG_SPL_SERIAL_SUPPORT) \
+			ret = -ENXIO;
-    && defined(CONFIG_SPL_LIBCOMMON_SUPPORT)    \
+		loader = spl_ll_find_loader(bootdev);
-    && !defined(CONFIG_SILENT_CONSOLE)
+		if (CONFIG_IS_ENABLED(SERIAL_SUPPORT) &&
-		if (loader)
+		    CONFIG_IS_ENABLED(LIBCOMMON_SUPPORT) &&
-			printf("Trying to boot from %s\n", loader->name);
+		    !IS_ENABLED(CONFIG_SILENT_CONSOLE)) {
-		else
+			if (loader)
-			puts(SPL_TPL_PROMPT "Unsupported Boot Device!\n");
+				printf("Trying to boot from %s\n",
-#endif
+				       spl_loader_name(loader));
+			else if (CONFIG_IS_ENABLED(SHOW_ERRORS))
+				printf(SPL_TPL_PROMPT
+				       "Unsupported Boot Device %d\n", bootdev);
+			else
+				puts(SPL_TPL_PROMPT "Unsupported Boot Device!\n");
+		}
 		if (loader && !spl_load_image(spl_image, loader)) {
-			spl_image->boot_device = spl_boot_list[i];
+			spl_image->boot_device = bootdev;
 			return 0;
 		}
 	}
 
-	return -ENODEV;
+	return ret;
 }
 
 #if defined(CONFIG_SPL_FRAMEWORK_BOARD_INIT_F)
@@ -710,9 +720,15 @@ void board_init_r(gd_t *dummy1, ulong dummy2)
 	spl_image.boot_device = BOOT_DEVICE_NONE;
 	board_boot_order(spl_boot_list);
 
-	if (boot_from_devices(&spl_image, spl_boot_list,
+	ret = boot_from_devices(&spl_image, spl_boot_list,
-			      ARRAY_SIZE(spl_boot_list))) {
+				ARRAY_SIZE(spl_boot_list));
-		puts(SPL_TPL_PROMPT "failed to boot from all boot devices\n");
+	if (ret) {
+		if (CONFIG_IS_ENABLED(SHOW_ERRORS) &&
+		    CONFIG_IS_ENABLED(LIBCOMMON_SUPPORT))
+			printf(SPL_TPL_PROMPT "failed to boot from all boot devices (err=%d)\n",
+			       ret);
+		else
+			puts(SPL_TPL_PROMPT "failed to boot from all boot devices\n");
 		hang();
 	}
 

include/spl.h

@@ -505,6 +505,16 @@ struct spl_image_loader {
 			  struct spl_boot_device *bootdev);
 };
 
+/* Helper function for accessing the name */
+static inline const char *spl_loader_name(const struct spl_image_loader *loader)
+{
+#ifdef CONFIG_SPL_LIBCOMMON_SUPPORT
+	return loader->name;
+#else
+	return NULL;
+#endif
+}
+
 /* Declare an SPL image loader */
 #define SPL_LOAD_IMAGE(__name)					\
 	ll_entry_declare(struct spl_image_loader, __name, spl_image_loader)