x86: Add an early CMOS access library

This adds a library that provides CMOS (inside RTC SRAM) access
at a very early stage when driver model is not available yet.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Stefan Roese <sr@denx.de>

arch/x86/include/asm/early_cmos.h

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2017, Bin Meng <bmeng.cn@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __EARLY_CMOS_H
+#define __EARLY_CMOS_H
+
+/* CMOS actually resides in the RTC SRAM */
+#define CMOS_IO_PORT	0x70
+
+/**
+ * cmos_read8() - Get 8-bit data stored at the given address
+ *
+ * This reads from CMOS for the 8-bit data stored at the given address.
+ *
+ * @addr:	RTC SRAM address
+ * @return:	8-bit data stored at the given address
+ */
+u8 cmos_read8(u8 addr);
+
+/**
+ * cmos_read16() - Get 16-bit data stored at the given address
+ *
+ * This reads from CMOS for the 16-bit data stored at the given address.
+ *
+ * @addr:	RTC SRAM address
+ * @return:	16-bit data stored at the given address
+ */
+u16 cmos_read16(u8 addr);
+
+/**
+ * cmos_read32() - Get 32-bit data stored at the given address
+ *
+ * This reads from CMOS for the 32-bit data stored at the given address.
+ *
+ * @addr:	RTC SRAM address
+ * @return:	32-bit data stored at the given address
+ */
+u32 cmos_read32(u8 addr);
+
+#endif /* __EARLY_CMOS_H */

arch/x86/lib/Makefile

@@ -15,6 +15,7 @@ obj-$(CONFIG_CMD_BOOTM) += bootm.o
 endif
 obj-y	+= cmd_boot.o
 obj-$(CONFIG_SEABIOS) += coreboot_table.o
+obj-y	+= early_cmos.o
 obj-$(CONFIG_EFI) += efi/
 obj-y	+= e820.o
 obj-y	+= gcc.o

arch/x86/lib/early_cmos.c

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2017, Bin Meng <bmeng.cn@gmail.com>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/*
+ * This library provides CMOS (inside RTC SRAM) access routines at a very
+ * early stage when driver model is not available yet. Only read access is
+ * provided. The 16-bit/32-bit read are compatible with driver model RTC
+ * uclass write ops, that data is stored in little-endian mode.
+ */
+
+#include <common.h>
+#include <asm/early_cmos.h>
+#include <asm/io.h>
+
+u8 cmos_read8(u8 addr)
+{
+	outb(addr, CMOS_IO_PORT);
+
+	return inb(CMOS_IO_PORT + 1);
+}
+
+u16 cmos_read16(u8 addr)
+{
+	u16 value = 0;
+	u16 data;
+	int i;
+
+	for (i = 0; i < sizeof(value); i++) {
+		data = cmos_read8(addr + i);
+		value |= data << (i << 3);
+	}
+
+	return value;
+}
+
+u32 cmos_read32(u8 addr)
+{
+	u32 value = 0;
+	u32 data;
+	int i;
+
+	for (i = 0; i < sizeof(value); i++) {
+		data = cmos_read8(addr + i);
+		value |= data << (i << 3);
+	}
+
+	return value;
+}