arch/x86: Add ebda read/write functions into EBDA library

This patch provides new APIs to write into EBDA area
and read from EBDA area based on user input structure.

Change-Id: I26d5c0ba82c842f0b734a8e0f03abf148737c5c4
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/21536
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Sumeet R Pawnikar <sumeet.r.pawnikar@intel.com>

src/arch/x86/ebda.c

@@ -20,6 +20,63 @@
 #include <arch/ebda.h>
 #include <arch/acpi.h>
 #include <commonlib/endian.h>
+#include <console/console.h>
+
+static void *get_ebda_start(void)
+{
+	return (void *)((uintptr_t)DEFAULT_EBDA_SEGMENT << 4);
+}
+
+static bool is_length_valid(size_t dlength)
+{
+	/* Check if input data length is > DEFAULT_EBDA_SIZE */
+	if (dlength > DEFAULT_EBDA_SIZE)
+		return false;
+
+	/* Valid data length */
+	return true;
+}
+
+/*
+ * EBDA area is representing a 1KB memory area just below
+ * the top of conventional memory (below 1MB)
+ */
+
+/*
+ * write_ebda_data is a wrapper function to write into EBDA area
+ *
+ * data = data to be written into EBDA area
+ * length = input data size.
+ */
+void write_ebda_data(const void *data, size_t length)
+{
+	void *ebda;
+
+	if (!is_length_valid(length))
+		die("Input data length is > EBDA default size (1KiB)!");
+
+	ebda = get_ebda_start();
+
+	memcpy(ebda, data, length);
+}
+
+/*
+ * read_ebda_data is a wrapper function to read from EBDA area
+ *
+ * data = data read from EBDA area based on input size
+ * length = read data size.
+ */
+void read_ebda_data(void *data, size_t length)
+{
+	void *ebda;
+
+	if (!is_length_valid(length))
+		die("Input data length is > EBDA default size (1KiB)!");
+
+	ebda = get_ebda_start();
+
+	memcpy(data, ebda, length);
+}
 
 void setup_ebda(u32 low_memory_size, u16 ebda_segment, u16 ebda_size)
 {
@@ -36,7 +93,7 @@ void setup_ebda(u32 low_memory_size, u16 ebda_segment, u16 ebda_size)
 
 	low_memory_kb = low_memory_size >> 10;
 	ebda_kb = ebda_size >> 10;
-	ebda = (void *)((uintptr_t)ebda_segment << 4);
+	ebda = get_ebda_start();
 
 	/* clear BIOS DATA AREA */
 	zero_n(X86_BDA_BASE, X86_BDA_SIZE);

src/arch/x86/include/arch/ebda.h

@@ -32,4 +32,24 @@
 void setup_ebda(u32 low_memory_size, u16 ebda_segment, u16 ebda_size);
 void setup_default_ebda(void);
 
+/*
+ * This read/write API only allows and assumes
+ * a single EBDA structure type for a platform.
+ */
+
+/*
+ * write_ebda_data is a wrapper function to write into EBDA area
+ *
+ * data = data to be written into EBDA area
+ * length = input data size.
+ */
+void write_ebda_data(const void *data, size_t length);
+/*
+ * read_ebda_data is a wrapper function to read from EBDA area
+ *
+ * data = data read from EBDA area based on input size
+ * length = read data size.
+ */
+void read_ebda_data(void *data, size_t length);
+
 #endif