xref: /titanic_41/usr/src/grub/grub-0.97/netboot/basemem.c (revision 1b8adde7ba7d5e04395c141c5400dc2cffd7d809)
1 #include "etherboot.h"
2 #define DEBUG_BASEMEM
3 /* Routines to allocate base memory in a BIOS-compatible way, by
4  * updating the Free Base Memory Size counter at 40:13h.
5  *
6  * Michael Brown <mbrown@fensystems.co.uk> (mcb30)
7  * $Id: basemem.c,v 1.5 2004/06/17 12:48:08 fengshuo Exp $
8  */
9 
10 #define fbms ( ( uint16_t * ) phys_to_virt ( 0x413 ) )
11 #define BASE_MEMORY_MAX ( 640 )
12 #define FREE_BLOCK_MAGIC ( ('!'<<0) + ('F'<<8) + ('R'<<16) + ('E'<<24) )
13 
14 typedef struct free_base_memory_block {
15 	uint32_t	magic;
16 	uint16_t	size_kb;
17 } free_base_memory_block_t;
18 
19 /* Return amount of free base memory in bytes
20  */
21 
get_free_base_memory(void)22 uint32_t get_free_base_memory ( void ) {
23 	return *fbms << 10;
24 }
25 
26 /* Adjust the real mode stack pointer.  We keep the real mode stack at
27  * the top of free base memory, rather than allocating space for it.
28  */
29 
adjust_real_mode_stack(void)30 static inline void adjust_real_mode_stack ( void ) {
31 /*  	real_mode_stack = ( *fbms << 10 ); */
32 }
33 
34 /* Allocate N bytes of base memory.  Amount allocated will be rounded
35  * up to the nearest kB, since that's the granularity of the BIOS FBMS
36  * counter.  Returns NULL if memory cannot be allocated.
37  */
38 
allot_base_memory(size_t size)39 void * allot_base_memory ( size_t size ) {
40 	uint16_t size_kb = ( size + 1023 ) >> 10;
41 	void *ptr = NULL;
42 
43 #ifdef DEBUG_BASEMEM
44 	printf ( "Trying to allocate %d kB of base memory, %d kB free\n",
45 		 size_kb, *fbms );
46 #endif
47 
48 	/* Free up any unused memory before we start */
49 	free_unused_base_memory();
50 
51 	/* Check available base memory */
52 	if ( size_kb > *fbms ) { return NULL; }
53 
54 	/* Reduce available base memory */
55 	*fbms -= size_kb;
56 
57 	/* Calculate address of memory allocated */
58 	ptr = phys_to_virt ( *fbms << 10 );
59 
60 #ifdef DEBUG_BASEMEM
61 	/* Zero out memory.  We do this so that allocation of
62 	 * already-used space will show up in the form of a crash as
63 	 * soon as possible.
64 	 */
65 	memset ( ptr, 0, size_kb << 10 );
66 #endif
67 
68 	/* Adjust real mode stack pointer */
69 	adjust_real_mode_stack ();
70 
71 	return ptr;
72 }
73 
74 /* Free base memory allocated by allot_base_memory.  The BIOS provides
75  * nothing better than a LIFO mechanism for freeing memory (i.e. it
76  * just has the single "total free memory" counter), but we improve
77  * upon this slightly; as long as you free all the allotted blocks, it
78  * doesn't matter what order you free them in.  (This will only work
79  * for blocks that are freed via forget_base_memory()).
80  *
81  * Yes, it's annoying that you have to remember the size of the blocks
82  * you've allotted.  However, since our granularity of allocation is
83  * 1K, the alternative is to risk wasting the occasional kB of base
84  * memory, which is a Bad Thing.  Really, you should be using as
85  * little base memory as possible, so consider the awkwardness of the
86  * API to be a feature! :-)
87  */
88 
forget_base_memory(void * ptr,size_t size)89 void forget_base_memory ( void *ptr, size_t size ) {
90 	uint16_t remainder = virt_to_phys(ptr) & 1023;
91 	uint16_t size_kb = ( size + remainder + 1023 ) >> 10;
92 	free_base_memory_block_t *free_block =
93 		( free_base_memory_block_t * ) ( ptr - remainder );
94 
95 	if ( ( ptr == NULL ) || ( size == 0 ) ) { return; }
96 
97 #ifdef DEBUG_BASEMEM
98 	printf ( "Trying to free %d bytes base memory at 0x%x\n",
99 		 size, virt_to_phys ( ptr ) );
100 	if ( remainder > 0 ) {
101 		printf ( "WARNING: destructively expanding free block "
102 			 "downwards to 0x%x\n",
103 			 virt_to_phys ( ptr - remainder ) );
104 	}
105 #endif
106 
107 	/* Mark every kilobyte within this block as free.  This is
108 	 * overkill for normal purposes, but helps when something has
109 	 * allocated base memory with a granularity finer than the
110 	 * BIOS granularity of 1kB.  PXE ROMs tend to do this when
111 	 * they allocate their own memory.  This method allows us to
112 	 * free their blocks (admittedly in a rather dangerous,
113 	 * tread-on-anything-either-side sort of way, but there's no
114 	 * other way to do it).
115 	 *
116 	 * Since we're marking every kB as free, there's actually no
117 	 * need for recording the size of the blocks.  However, we
118 	 * keep this in so that debug messages are friendlier.  It
119 	 * probably adds around 8 bytes to the overall code size.
120 	 */
121 	while ( size_kb > 0 ) {
122 		/* Mark this block as unused */
123 		free_block->magic = FREE_BLOCK_MAGIC;
124 		free_block->size_kb = size_kb;
125 		/* Move up by 1 kB */
126 		free_block = (void *)free_block + ( 1 << 10 );
127 		size_kb--;
128 	}
129 
130 	/* Free up unused base memory */
131 	free_unused_base_memory();
132 }
133 
134 /* Do the actual freeing of memory.  This is split out from
135  * forget_base_memory() so that it may be called separately.  It
136  * should be called whenever base memory is deallocated by an external
137  * entity (if we can detect that it has done so) so that we get the
138  * chance to free up our own blocks.
139  */
free_unused_base_memory(void)140 void free_unused_base_memory ( void ) {
141 	free_base_memory_block_t *free_block = NULL;
142 
143 	/* Try to release memory back to the BIOS.  Free all
144 	 * consecutive blocks marked as free.
145 	 */
146 	while ( 1 ) {
147 		/* Calculate address of next potential free block */
148 		free_block = ( free_base_memory_block_t * )
149 			phys_to_virt ( *fbms << 10 );
150 
151 		/* Stop processing if we're all the way up to 640K or
152 		 * if this is not a free block
153 		 */
154 		if ( ( *fbms == BASE_MEMORY_MAX ) ||
155 		     ( free_block->magic != FREE_BLOCK_MAGIC ) ) {
156 			break;
157 		}
158 
159 		/* Return memory to BIOS */
160 		*fbms += free_block->size_kb;
161 
162 #ifdef DEBUG_BASEMEM
163 		printf ( "Freed %d kB base memory, %d kB now free\n",
164 			 free_block->size_kb, *fbms );
165 
166 		/* Zero out freed block.  We do this in case
167 		 * the block contained any structures that
168 		 * might be located by scanning through
169 		 * memory.
170 		 */
171 		memset ( free_block, 0, free_block->size_kb << 10 );
172 #endif
173 	}
174 
175 	/* Adjust real mode stack pointer */
176 	adjust_real_mode_stack ();
177 }
178 
179