[PATCH] arm: mediatek: mt7988: restore full DRAM bank reporting

[Rudy Andram]

MT7988 detects the full installed DRAM in dram_init(), but after
commit bddd6bbef3dc ("arm: mediatek: mt7988: drop dram_init_banksize()")
it fell back to the generic dram_init_banksize() implementation.

That generic path populates bd->bi_dram[0].size with
get_effective_memsize(), which is capped by CFG_MAX_MEM_MAPPED. On
MT7988 this limits the exported DRAM bank to 3 GiB even when 8 GiB is
installed.

As a result, U-Boot reports the full DRAM in gd->ram_size but exposes
only the low 3 GiB through bd->bi_dram[]. This truncated map can then
propagate to later stages through memory handoff and DT fixups.

On a Banana Pi R4 Pro 8G (MT7988), bdinfo shows:

Before:
  DRAM bank   = 0x000000000
  -> start    = 0x0000000040000000
  -> size     = 0x00000000c0000000

After:
  DRAM bank   = 0x000000000
  -> start    = 0x0000000040000000
  -> size     = 0x0000000200000000

Restore the MT7988-specific dram_init_banksize() implementation so
bd->bi_dram[0] publishes gd->ram_base and gd->ram_size again.

Version tested
U-Boot 2026.07-rc2-bpi-g6a1580973a11-dirty (May 27 2026 - 14:39:18 +0000)

Fixes: bddd6bbef3dc ("arm: mediatek: mt7988: drop dram_init_banksize()")
Tested-by: Rudy Andram <rmandrad at gmail.com>
Signed-off-by: Rudy Andram <rmandrad at gmail.com>
---
 arch/arm/mach-mediatek/mt7988/init.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm/mach-mediatek/mt7988/init.c b/arch/arm/mach-mediatek/mt7988/init.c
index 7f4d934bfe9..08eb73d42b1 100644
--- a/arch/arm/mach-mediatek/mt7988/init.c
+++ b/arch/arm/mach-mediatek/mt7988/init.c
@@ -26,6 +26,15 @@ int dram_init(void)
 	return 0;
 }
 
+int dram_init_banksize(void)
+{
+	/* Report the full detected DRAM size to later stages. */
+	gd->bd->bi_dram[0].start = gd->ram_base;
+	gd->bd->bi_dram[0].size = gd->ram_size;
+
+	return 0;
+}
+
 void reset_cpu(ulong addr)
 {
 	psci_system_reset();
-- 
2.54.0