U-Boot

// SPDX-License-Identifier: GPL-2.0+
/*
 * (C) Copyright 2004
 * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 */

#include <common.h>
#include <init.h>
#include <asm/global_data.h>

DECLARE_GLOBAL_DATA_PTR;

#ifdef __PPC__
/*
 * At least on G2 PowerPC cores, sequential accesses to non-existent
 * memory must be synchronized.
 */
# include <asm/io.h>	/* for sync() */
#else
# define sync()		/* nothing */
#endif

/*
 * Check memory range for valid RAM. A simple memory test determines
 * the actually available RAM size between addresses `base' and
 * `base + maxsize'.
 */
long get_ram_size(long *base, long maxsize)
{
	volatile long *addr;
	long           save[BITS_PER_LONG - 1];
	long           save_base;
	long           cnt;
	long           val;
	long           size;
	int            i = 0;

	for (cnt = (maxsize / sizeof(long)) >> 1; cnt > 0; cnt >>= 1) {
		addr = base + cnt;	/* pointer arith! */
		sync();
		save[i++] = *addr;
		sync();
		*addr = ~cnt;
	}

	addr = base;
	sync();
	save_base = *addr;
	sync();
	*addr = 0;

	sync();
	if ((val = *addr) != 0) {
		/* Restore the original data before leaving the function. */
		sync();
		*base = save_base;
		for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
			addr  = base + cnt;
			sync();
			*addr = save[--i];
		}
		return (0);
	}

	for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
		addr = base + cnt;	/* pointer arith! */
		val = *addr;
		*addr = save[--i];
		if (val != ~cnt) {
			size = cnt * sizeof(long);
			/*
			 * Restore the original data
			 * before leaving the function.
			 */
			for (cnt <<= 1;
			     cnt < maxsize / sizeof(long);
			     cnt <<= 1) {
				addr  = base + cnt;
				*addr = save[--i];
			}
			/* warning: don't restore save_base in this case,
			 * it is already done in the loop because
			 * base and base+size share the same physical memory
			 * and *base is saved after *(base+size) modification
			 * in first loop
			 */
			return (size);
		}
	}
	*base = save_base;

	return (maxsize);
}

phys_size_t __weak get_effective_memsize(void)
{
	phys_size_t ram_size = gd->ram_size;

#ifdef CONFIG_MPC85xx
	/*
	 * Check for overflow and limit ram size to some representable value.
	 * It is required that ram_base + ram_size must be representable by
	 * phys_size_t type and must be aligned by direct access, therefore
	 * calculate it from last 4kB sector which should work as alignment
	 * on any platform.
	 */
	if (gd->ram_base + ram_size < gd->ram_base)
		ram_size = ((phys_size_t)~0xfffULL) - gd->ram_base;
#endif

#ifndef CFG_MAX_MEM_MAPPED
	return ram_size;
#else
	/* limit stack to what we can reasonable map */
	return ((ram_size > CFG_MAX_MEM_MAPPED) ?
		CFG_MAX_MEM_MAPPED : ram_size);
#endif
}