target: add function to get number of bytes available in working area

This is a much cleaner solution to the problem of allocating as much
working area as possible than what is currently being done in most/all flash
drivers (which is: try an arbitrary sized chunk, if it fails, pick a smaller
number, rinse and repeat).

Use this function to find out how much working area is available, limit or
restrict that amount at will and then simply allocate it.

Change-Id: Ib7d5d0b7485aed3e0a4fad60c1bedb7dfd16146f
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/446
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/target/target.c

@@ -1502,6 +1502,25 @@ void target_free_all_working_areas(struct target *target)
 	target_free_all_working_areas_restore(target, 1);
 }
 
+/* Find the largest number of bytes that can be allocated */
+uint32_t target_get_working_area_avail(struct target *target)
+{
+	struct working_area *c = target->working_areas;
+	uint32_t max_size = 0;
+
+	if (c == NULL)
+		return target->working_area_size;
+
+	while (c) {
+		if (c->free && max_size < c->size)
+			max_size = c->size;
+
+		c = c->next;
+	}
+
+	return max_size;
+}
+
 int target_arch_state(struct target *target)
 {
 	int retval;

src/target/target.h

@@ -540,6 +540,7 @@ int target_alloc_working_area_try(struct target *target,
 		uint32_t size, struct working_area **area);
 int target_free_working_area(struct target *target, struct working_area *area);
 void target_free_all_working_areas(struct target *target);
+uint32_t target_get_working_area_avail(struct target *target);
 
 extern struct target *all_targets;