[U-Boot] [RFC v2] env: Fix errors printing on env loading

[Sam Protsenko]

This is just a draft to discuss ideas related to "Make U-Boot log great
again" thread.

With this patch we will have something like this:

    Attempting to load environment from FAT:
      -> MMC: no card present
      -> ** Bad device mmc 0 **
      -> Failed (-5)
    Attempting to load environment from MMC: OK

instead of this:

    Loading Environment from FAT... MMC: no card present
    ** Bad device mmc 0 **
    Failed (-5)
    Loading Environment from MMC... OK

Two things were done in this patch:
 - print messages from drivers in nested style (with "->" prefix); to do
   so, add GD_FLG_PR_PREFIX flag and check it in puts()
 - make "OK" to be printed on the same line as main message; to do so,
   issue ASCII escape codes [1] to move cursor back to main message line

[1] https://en.wikipedia.org/wiki/ANSI_escape_code#CSI_sequences

Signed-off-by: Sam Protsenko <semen.protsenko at linaro.org>
---
 common/console.c                  |  6 ++++++
 env/env.c                         | 17 +++++++++++++----
 include/asm-generic/global_data.h |  1 +
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/common/console.c b/common/console.c
index 2ba33dc574..a0db0ffea6 100644
--- a/common/console.c
+++ b/common/console.c
@@ -533,6 +533,12 @@ void putc(const char c)
 
 void puts(const char *s)
 {
+	if (gd->flags & GD_FLG_PR_PREFIX) {
+		gd->flags &= ~GD_FLG_PR_PREFIX;
+		puts("  -> ");
+		gd->flags |= GD_FLG_PR_PREFIX;
+	}
+
 #ifdef CONFIG_DEBUG_UART
 	if (!gd || !(gd->flags & GD_FLG_SERIAL_READY)) {
 		while (*s) {
diff --git a/env/env.c b/env/env.c
index 5c0842ac07..ff044ccee1 100644
--- a/env/env.c
+++ b/env/env.c
@@ -187,6 +187,7 @@ int env_load(void)
 
 	for (prio = 0; (drv = env_driver_lookup(ENVOP_LOAD, prio)); prio++) {
 		int ret;
+		char msg[75];
 
 		if (!drv->load)
 			continue;
@@ -194,12 +195,20 @@ int env_load(void)
 		if (!env_has_inited(drv->location))
 			continue;
 
-		printf("Loading Environment from %s... ", drv->name);
+		snprintf(msg, 75, "Attempting to load environment from %s:\n",
+			 drv->name);
+		puts(msg);
+		gd->flags |= GD_FLG_PR_PREFIX;
 		ret = drv->load();
-		if (ret)
+		if (ret) {
 			printf("Failed (%d)\n", ret);
-		else
-			printf("OK\n");
+			gd->flags &= ~GD_FLG_PR_PREFIX;
+		} else {
+			size_t len = strlen(msg);
+
+			gd->flags &= ~GD_FLG_PR_PREFIX;
+			printf("\033[1A\033[%zuC OK\n", len - 1);
+		}
 
 		if (!ret)
 			return 0;
diff --git a/include/asm-generic/global_data.h b/include/asm-generic/global_data.h
index 0fd4900392..7e83617664 100644
--- a/include/asm-generic/global_data.h
+++ b/include/asm-generic/global_data.h
@@ -150,5 +150,6 @@ typedef struct global_data {
 #define GD_FLG_ENV_DEFAULT	0x02000 /* Default variable flag	   */
 #define GD_FLG_SPL_EARLY_INIT	0x04000 /* Early SPL init is done	   */
 #define GD_FLG_LOG_READY	0x08000 /* Log system is ready for use	   */
+#define GD_FLG_PR_PREFIX	0x10000	/* Print prefix before message	   */
 
 #endif /* __ASM_GENERIC_GBL_DATA_H */
-- 
2.18.0