dlmalloc: do memset in malloc init as new default config

This commit introduces new config: CONFIG_SYS_MALLOC_CLEAR_ON_INIT.

This config is an expert option and is enabled by default.

The all amount of memory reserved for the malloc, is by default set
to zero in mem_malloc_init(). When the malloc reserved memory exceeds
few MiB, then the boot process can slow down.

So disabling this config, is an expert option to reduce the boot time,
and can be disabled by Kconfig.

Note:
After disable this option, only calloc() will return the pointer
to the zeroed memory area. Previously, without this option,
the memory pointed to untouched malloc memory region, was filled
with zeros. So it means, that code with malloc() calls should
be reexamined.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

Kconfig

@@ -72,13 +72,31 @@ config SYS_MALLOC_F_LEN
 	  initial serial device and any others that are needed.
 
 menuconfig EXPERT
-        bool "Configure standard U-Boot features (expert users)"
-        help
-          This option allows certain base U-Boot options and settings
-          to be disabled or tweaked. This is for specialized
-          environments which can tolerate a "non-standard" U-Boot.
-          Only use this if you really know what you are doing.
-
+	bool "Configure standard U-Boot features (expert users)"
+	default y
+	help
+	  This option allows certain base U-Boot options and settings
+	  to be disabled or tweaked. This is for specialized
+	  environments which can tolerate a "non-standard" U-Boot.
+	  Only use this if you really know what you are doing.
+
+if EXPERT
+	config SYS_MALLOC_CLEAR_ON_INIT
+	bool "Init with zeros the memory reserved for malloc (slow)"
+	default y
+	help
+	  This setting is enabled by default. The reserved malloc
+	  memory is initialized with zeros, so first malloc calls
+	  will return the pointer to the zeroed memory. But this
+	  slows the boot time.
+
+	  It is recommended to disable it, when CONFIG_SYS_MALLOC_LEN
+	  value, has more than few MiB, e.g. when uses bzip2 or bmp logo.
+	  Then the boot time can be significantly reduced.
+	  Warning:
+	  When disabling this, please check if malloc calls, maybe
+	  should be replaced by calloc - if expects zeroed memory.
+endif
 endmenu		# General setup
 
 menu "Boot images"

common/dlmalloc.c

@@ -1535,9 +1535,9 @@ void mem_malloc_init(ulong start, ulong size)
 
 	debug("using memory %#lx-%#lx for malloc()\n", mem_malloc_start,
 	      mem_malloc_end);
-
-	memset((void *)mem_malloc_start, 0, size);
-
+#ifdef CONFIG_SYS_MALLOC_CLEAR_ON_INIT
+	memset((void *)mem_malloc_start, 0x0, size);
+#endif
 	malloc_bin_reloc();
 }
 
@@ -2948,9 +2948,11 @@ Void_t* cALLOc(n, elem_size) size_t n; size_t elem_size;
 
 
   /* check if expand_top called, in which case don't need to clear */
+#ifdef CONFIG_SYS_MALLOC_CLEAR_ON_INIT
 #if MORECORE_CLEARS
   mchunkptr oldtop = top;
   INTERNAL_SIZE_T oldtopsize = chunksize(top);
+#endif
 #endif
   Void_t* mem = mALLOc (sz);
 
@@ -2977,12 +2979,14 @@ Void_t* cALLOc(n, elem_size) size_t n; size_t elem_size;
 
     csz = chunksize(p);
 
+#ifdef CONFIG_SYS_MALLOC_CLEAR_ON_INIT
 #if MORECORE_CLEARS
     if (p == oldtop && csz > oldtopsize)
     {
       /* clear only the bytes from non-freshly-sbrked memory */
       csz = oldtopsize;
     }
+#endif
 #endif
 
     MALLOC_ZERO(mem, csz - SIZE_SZ);