1 /* SPDX-License-Identifier: GPL-2.0-only */
2
3 #include <types.h>
4 #include <symbols.h>
5 #include <device/mmio.h>
6 #include <ramdetect.h>
7 #include <console/console.h>
8
9 #define OVERLAP(a, b, s, e) ((b) > (s) && (a) < (e))
10
probe_mb(const uintptr_t dram_start,const uintptr_t size)11 int __weak probe_mb(const uintptr_t dram_start, const uintptr_t size)
12 {
13 uintptr_t addr = dram_start + (size * MiB) - sizeof(uint32_t);
14 static const uint32_t patterns[] = {0x55aa55aa, 0x12345678};
15 void *ptr = (void *)addr;
16 size_t i;
17
18 /* Don't accidentally clobber oneself. */
19 if (OVERLAP(addr, addr + sizeof(uint32_t), (uintptr_t)_program, (uintptr_t)_eprogram))
20 return 1;
21
22 uint32_t old = read32(ptr);
23 for (i = 0; i < ARRAY_SIZE(patterns); i++) {
24 write32(ptr, patterns[i]);
25 if (read32(ptr) != patterns[i])
26 break;
27 }
28
29 write32(ptr, old);
30 return i == ARRAY_SIZE(patterns);
31 }
32
33 /* - 20 as probe_size is in MiB, - 1 as i is signed */
34 #define MAX_ADDRESSABLE_SPACE (sizeof(size_t) * 8 - 20 - 1)
35
36 /* Probe an area if it's read/writable. */
probe_ramsize(const uintptr_t dram_start,const size_t probe_size)37 size_t probe_ramsize(const uintptr_t dram_start, const size_t probe_size)
38 {
39 ssize_t i;
40 size_t msb = 0;
41 size_t discovered = 0;
42
43 static size_t saved_result;
44 if (saved_result)
45 return saved_result;
46
47 /* Find the MSB + 1. */
48 size_t tmp = probe_size;
49 do {
50 msb++;
51 } while (tmp >>= 1);
52
53 /* Limit search to accessible address space */
54 msb = MIN(msb, MAX_ADDRESSABLE_SPACE);
55
56 /* Compact binary search. */
57 for (i = msb; i >= 0; i--) {
58 if ((discovered | (1ULL << i)) > probe_size)
59 continue;
60 if (probe_mb(dram_start, (discovered | (1ULL << i))))
61 discovered |= (1ULL << i);
62 }
63
64 saved_result = discovered;
65 printk(BIOS_DEBUG, "RAMDETECT: Found %zu MiB RAM\n", discovered);
66 return discovered;
67 }
68