dfu: define a callback function for the dfu_alt_info environment variable

I'm trying to use dfu-util for bootstrapping an stm32mp board. It
mostly works fine, but something goes horribly wrong as soon as I make
use of the ability to run arbitrary u-boot shell commands. The shell
commands themselves work fine, but the heuristic "dfu_alt_info may
have changed, we have to reinit" seems to cause the board and/or my
host machine to go into some bad state, and further dfu-util commands
fail.

U-Boot already has a mechanism whereby C code can be told about
changes to specific environment variables. So instead of always doing
re-init, add a hook to the dfu_alt_info variable so that we only do
set dfu_reinit_needed if the commands actually did modify that
variable.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20240911133900.1444083-1-rasmus.villemoes@prevas.dk
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>

drivers/dfu/dfu.c

@@ -27,6 +27,21 @@ static unsigned long dfu_timeout = 0;
 #endif
 
 bool dfu_reinit_needed = false;
+bool dfu_alt_info_changed = false;
+
+static int on_dfu_alt_info(const char *name, const char *value, enum env_op op,
+			   int flags)
+{
+	switch (op) {
+	case env_op_create:
+	case env_op_overwrite:
+	case env_op_delete:
+		dfu_alt_info_changed = true;
+		break;
+	}
+	return 0;
+}
+U_BOOT_ENV_CALLBACK(dfu_alt_info, on_dfu_alt_info);
 
 /*
  * The purpose of the dfu_flush_callback() function is to
@@ -152,6 +167,7 @@ int dfu_init_env_entities(char *interface, char *devstr)
 	int ret = 0;
 
 	dfu_reinit_needed = false;
+	dfu_alt_info_changed = false;
 
 #ifdef CONFIG_SET_DFU_ALT_INFO
 	set_dfu_alt_info(interface, devstr);

drivers/dfu/dfu_mmc.c

@@ -232,7 +232,8 @@ int dfu_flush_medium_mmc(struct dfu_entity *dfu)
 		break;
 	case DFU_SCRIPT:
 		/* script may have changed the dfu_alt_info */
-		dfu_reinit_needed = true;
+		if (dfu_alt_info_changed)
+			dfu_reinit_needed = true;
 		break;
 	case DFU_RAW_ADDR:
 	case DFU_SKIP:

include/dfu.h

@@ -517,6 +517,7 @@ static inline int dfu_fill_entity_virt(struct dfu_entity *dfu, char *devstr,
 #endif
 
 extern bool dfu_reinit_needed;
+extern bool dfu_alt_info_changed;
 
 #if CONFIG_IS_ENABLED(DFU_WRITE_ALT)
 /**

include/env_callback.h

@@ -69,6 +69,12 @@
 #define BOOTSTD_CALLBACK
 #endif
 
+#ifdef CONFIG_DFU
+#define DFU_CALLBACK "dfu_alt_info:dfu_alt_info,"
+#else
+#define DFU_CALLBACK
+#endif
+
 /*
  * This list of callback bindings is static, but may be overridden by defining
  * a new association in the ".callbacks" environment variable.
@@ -79,6 +85,7 @@
 	NET_CALLBACKS \
 	NET6_CALLBACKS \
 	BOOTSTD_CALLBACK \
+	DFU_CALLBACK \
 	"loadaddr:loadaddr," \
 	SILENT_CALLBACK \
 	"stdin:console,stdout:console,stderr:console," \