ramdetect.c

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/* SPDX-License-Identifier: GPL-2.0-only */
 
#include <types.h>
#include <symbols.h>
#include <device/mmio.h>
#include <ramdetect.h>
#include <console/console.h>
 
#define OVERLAP(a, b, s, e) ((b) > (s) && (a) < (e))
 
int __weak probe_mb(const uintptr_t dram_start, const uintptr_t size)
{
        uintptr_t addr = dram_start + (size * MiB) - sizeof(uint32_t);
        static const uint32_t patterns[] = {
                0x55aa55aa,
                0x12345678
        };
        void *ptr = (void *) addr;
        size_t i;
 
        /* Don't accidentally clober oneself. */
        if (OVERLAP(addr, addr + sizeof(uint32_t), (uintptr_t)_program, (uintptr_t) _eprogram))
                return 1;
 
        uint32_t old = read32(ptr);
        for (i = 0; i < ARRAY_SIZE(patterns); i++) {
                write32(ptr, patterns[i]);
                if (read32(ptr) != patterns[i])
                        break;
        }
 
        write32(ptr, old);
        return i == ARRAY_SIZE(patterns);
}
 
/* - 20 as probe_size is in MiB, - 1 as i is signed */
#define MAX_ADDRESSABLE_SPACE (sizeof(size_t) * 8 - 20 - 1)
 
/* Probe an area if it's read/writable. */
size_t probe_ramsize(const uintptr_t dram_start, const size_t probe_size)
{
        ssize_t i;
        size_t msb = 0;
        size_t discovered = 0;
 
        static size_t saved_result;
        if (saved_result)
                return saved_result;
 
        /* Find the MSB + 1. */
        size_t tmp = probe_size;
        do {
                msb++;
        } while (tmp >>= 1);
 
        /* Limit search to accessible address space */
        msb = MIN(msb, MAX_ADDRESSABLE_SPACE);
 
        /* Compact binary search.  */
        for (i = msb; i >= 0; i--)
                if (probe_mb(dram_start, (discovered | (1ULL << i))))
                        discovered |= (1ULL << i);
 
        saved_result = discovered;
        printk(BIOS_DEBUG, "RAMDETECT: Found %zu MiB RAM\n", discovered);
        return discovered;
}