[PATCH v2 3/4] fdtdec: Introduce fdtdec_setup_ram_size() to determine the memory size

[Ilias Apalodimas]

We previously added a fdtdec_setup_mem_ram_top() to determine the
topmost address of the last DRAM bank. Similarly the overall memory
size must be calculated when U-Boot gets relocated to the actual end of
all available DRAM.

Pre-patch:
U-Boot 2026.04-rc5-00012-g5789f787c8a6-dirty (Mar 31 2026 - 09:13:34 +0300)
DRAM:  4 GiB (total 8 GiB)

Post-patch:
U-Boot 2026.04-rc5-00012-g5789f787c8a6 (Mar 31 2026 - 09:12:59 +0300)
DRAM:  8 GiB

Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
 include/fdtdec.h | 15 +++++++++++++++
 lib/fdtdec.c     | 18 ++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/include/fdtdec.h b/include/fdtdec.h
index 26e40c3cdb46..9bccd70bbdb6 100644
--- a/include/fdtdec.h
+++ b/include/fdtdec.h
@@ -965,6 +965,21 @@ int fdtdec_setup_mem_ram_top(void);
  * invalid
  */
 int fdtdec_setup_memory_banksize(void);
+/**
+ * fdtdec_setup_ram_size() - decode and setup setup gd->ram_size to the sum of
+ *			     all banks
+ *
+ * Decode the /memory 'reg' property to determine the memory available in all
+ * banks and populate the global data ram_size with it.
+ *
+ * This function should be called from a boards board_get_usable_ram_top().
+ * This helper function allows for boards to query the device tree for the
+ * overall memory described in as the sum of all memory banks.
+ *
+ * Return: 0 if OK, -EINVAL if the /memory node or reg property is missing or
+ * invalid
+ */
+int fdtdec_setup_ram_size(void);
 
 /**
  * fdtdec_set_ethernet_mac_address() - set MAC address for default interface
diff --git a/lib/fdtdec.c b/lib/fdtdec.c
index bdb26d8fb75b..715662d27a8c 100644
--- a/lib/fdtdec.c
+++ b/lib/fdtdec.c
@@ -1142,6 +1142,24 @@ int fdtdec_setup_memory_banksize(void)
 	return fdtdec_setup_mem_for_each_bank(fdtdec_setup_memory_banksize_bankfn);
 }
 
+static void fdtdec_setup_total_ram_fn(struct resource *res, int bank)
+{
+	gd->ram_size += res->end - res->start + 1;
+}
+
+int fdtdec_setup_ram_size(void)
+{
+	int ret;
+	phys_addr_t old_size = gd->ram_size;
+
+	gd->ram_size = 0;
+	ret = fdtdec_setup_mem_for_each_bank(fdtdec_setup_total_ram_fn);
+	if (ret)
+		gd->ram_size = old_size;
+
+	return ret;
+}
+
 static void fdtdec_setup_mem_size_base_lowest_bankfn(struct resource *res, int bank)
 {
 	unsigned long base = (unsigned long)res->start;
-- 
2.53.0