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lmb: Optionally limit available memory to 4 GiB on limited systems

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Some architectures can not DMA above 4 GiB boundary,
limit available memory to memory below 4 GiB boundary.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> #rpi4 8GiB
This commit is contained in:
Marek Vasut
2026-06-03 16:17:55 +02:00
committed by Tom Rini
parent 4065ee552b
commit af4aad1f0a
2 changed files with 27 additions and 1 deletions
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8
lib/Kconfig
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@@ -1295,6 +1295,14 @@ config SPL_LMB_ARCH_MEM_MAP
memory map. Enable this config in such scenarios which allow
architectures and boards to define their own memory map.
config LMB_LIMIT_DMA_BELOW_4G
bool
depends on LMB
default y if ARCH_BCM283X
help
Some architectures can not DMA above 4 GiB boundary,
limit available memory to memory below 4 GiB boundary.
config PHANDLE_CHECK_SEQ
bool "Enable phandle check while getting sequence number"
help

20
lib/lmb.c
View File

@@ -611,6 +611,7 @@ static __maybe_unused void lmb_reserve_common_spl(void)
static void lmb_add_memory(void)
{
int i;
phys_addr_t bank_end;
phys_size_t size;
u64 ram_top = gd->ram_top;
struct bd_info *bd = gd->bd;
@@ -625,8 +626,25 @@ static void lmb_add_memory(void)
for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {
size = bd->bi_dram[i].size;
if (size)
if (size) {
lmb_add(bd->bi_dram[i].start, size);
if (!IS_ENABLED(CONFIG_LMB_LIMIT_DMA_BELOW_4G))
continue;
bank_end = bd->bi_dram[i].start + size;
/*
* Reserve memory above ram_top as
* no-overwrite so that it cannot be
* allocated
*/
if (bd->bi_dram[i].start >= ram_top)
lmb_reserve(bd->bi_dram[i].start, size,
LMB_NOOVERWRITE);
else if (bank_end > ram_top)
lmb_reserve(ram_top, bank_end - ram_top,
LMB_NOOVERWRITE);
}
}
}