src/lib/ramdetect.c

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