[PATCH v2] board_f: show_dram_config: Print also real DRAM size

[Pali Rohár]

32-bit U-Boot builds cannot use more than around 2 GB of DDR memory. But on
some platforms/boards it is possible to connect also 4 GB SODIMM DDR memory.
U-Boot currently prints only effective size of RAM which can use, which may
be misleading as somebody would expect that this line prints total size of
connected DDR modules. So change show_dram_config code to prints both real
and effective DRAM size if they are different. If they are same then print
just one number like before. It is possible that effective size is just few
bytes smaller than the real size, so print both numbers only in case
function print_size() prints formats them differently.

Signed-off-by: Pali Rohár <pali at kernel.org>

---
Changes in v2:
* Move calculation code into separate macro and add description of it
---
 common/board_f.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/common/board_f.c b/common/board_f.c
index 9e34fbee147e..88a6dfff03fc 100644
--- a/common/board_f.c
+++ b/common/board_f.c
@@ -54,6 +54,7 @@
 #include <asm/sections.h>
 #include <dm/root.h>
 #include <linux/errno.h>
+#include <linux/log2.h>
 
 /*
  * Pointer to initial global data area
@@ -213,6 +214,36 @@ static int announce_dram_init(void)
 	return 0;
 }
 
+/*
+ * From input size calculate its nearest rounded unit scale (multiply of 2^10)
+ * and value in calculated unit scale multiplied by 10 (as fractional fixed
+ * point number with one decimal digit), which is human natural format,
+ * same what uses print_size() function for displaying. Mathematically it is:
+ * round_nearest(val * 2^scale) = size * 10; where: 10 <= val < 10240.
+ *
+ * For example for size=87654321 we calculate scale=20 and val=836 which means
+ * that input has natural human format 83.6 M (mega = 2^20).
+ */
+#define compute_size_scale_val(size, scale, val) do { \
+	scale = ilog2(size) / 10 * 10; \
+	val = (10 * size + ((1ULL << scale) >> 1)) >> scale; \
+	if (val == 10240) { val = 10; scale += 10; } \
+} while (0)
+
+/*
+ * Check if the sizes in their natural units written in decimal format with
+ * one fraction number are same.
+ */
+static int sizes_near(unsigned long long size1, unsigned long long size2)
+{
+	unsigned int size1_scale, size1_val, size2_scale, size2_val;
+
+	compute_size_scale_val(size1, size1_scale, size1_val);
+	compute_size_scale_val(size2, size2_scale, size2_val);
+
+	return size1_scale == size2_scale && size1_val == size2_val;
+}
+
 static int show_dram_config(void)
 {
 	unsigned long long size;
@@ -229,7 +260,11 @@ static int show_dram_config(void)
 	}
 	debug("\nDRAM:  ");
 
-	print_size(size, "");
+	print_size(gd->ram_size, "");
+	if (!sizes_near(gd->ram_size, size)) {
+		printf(" (effective ");
+		print_size(size, ")");
+	}
 	board_add_ram_info(0);
 	putc('\n');
 
-- 
2.20.1