drivers/rtc: add support for Microchip MCP795

Add driver for SPI RTC Microchip MCP795.  Only supports saving/loading
time from the chip (i.  e.  no alarms/power events/ID).

Signed-off-by: Josef Gajdusek <atx@atx.name>
Cc: Jingoo Han <jg1.han@samsung.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 208 insertions, 0 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index a27958de11ff..486d34b225d5 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -661,6 +661,14 @@ config RTC_DRV_RX4581
           This driver can also be built as a module. If so the module
           will be called rtc-rx4581.
 
+config RTC_DRV_MCP795
+        tristate "Microchip MCP795"
+        help
+          If you say yes here you will get support for the Microchip MCP795.
+
+          This driver can also be built as a module. If so the module
+          will be called rtc-mcp795.
+
 endif # SPI_MASTER
 
 comment "Platform RTC drivers"
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 660ab296b956..9d7775534a3d 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -81,6 +81,7 @@ obj-$(CONFIG_RTC_DRV_MAX8997)	+= rtc-max8997.o
 obj-$(CONFIG_RTC_DRV_MAX6902)   += rtc-max6902.o
 obj-$(CONFIG_RTC_DRV_MAX77686)  += rtc-max77686.o
 obj-$(CONFIG_RTC_DRV_MC13XXX)   += rtc-mc13xxx.o
+obj-$(CONFIG_RTC_DRV_MCP795)    += rtc-mcp795.o
 obj-$(CONFIG_RTC_DRV_MSM6242)   += rtc-msm6242.o
 obj-$(CONFIG_RTC_DRV_MPC5121)   += rtc-mpc5121.o
 obj-$(CONFIG_RTC_DRV_MV)        += rtc-mv.o
diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
new file mode 100644
index 000000000000..34295bf00416
--- /dev/null
+++ b/drivers/rtc/rtc-mcp795.c
@@ -0,0 +1,199 @@
+/*
+ * SPI Driver for Microchip MCP795 RTC
+ *
+ * Copyright (C) Josef Gajdusek <atx@atx.name>
+ *
+ * based on other Linux RTC drivers
+ *
+ * Device datasheet:
+ * http://ww1.microchip.com/downloads/en/DeviceDoc/22280A.pdf
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/printk.h>
+#include <linux/spi/spi.h>
+#include <linux/rtc.h>
+
+/* MCP795 Instructions, see datasheet table 3-1 */
+#define MCP795_EEREAD   0x03
+#define MCP795_EEWRITE  0x02
+#define MCP795_EEWRDI   0x04
+#define MCP795_EEWREN   0x06
+#define MCP795_SRREAD   0x05
+#define MCP795_SRWRITE  0x01
+#define MCP795_READ             0x13
+#define MCP795_WRITE    0x12
+#define MCP795_UNLOCK   0x14
+#define MCP795_IDWRITE  0x32
+#define MCP795_IDREAD   0x33
+#define MCP795_CLRWDT   0x44
+#define MCP795_CLRRAM   0x54
+
+#define MCP795_ST_BIT   0x80
+#define MCP795_24_BIT   0x40
+
+static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
+{
+        struct spi_device *spi = to_spi_device(dev);
+        int ret;
+        u8 tx[2];
+
+        tx[0] = MCP795_READ;
+        tx[1] = addr;
+        ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
+
+        if (ret)
+                dev_err(dev, "Failed reading %d bytes from address %x.\n",
+                                        count, addr);
+
+        return ret;
+}
+
+static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
+{
+        struct spi_device *spi = to_spi_device(dev);
+        int ret;
+        u8 tx[2 + count];
+
+        tx[0] = MCP795_WRITE;
+        tx[1] = addr;
+        memcpy(&tx[2], data, count);
+
+        ret = spi_write(spi, tx, 2 + count);
+
+        if (ret)
+                dev_err(dev, "Failed to write %d bytes to address %x.\n",
+                                        count, addr);
+
+        return ret;
+}
+
+static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
+{
+        int ret;
+        u8 tmp;
+
+        ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
+        if (ret)
+                return ret;
+
+        if ((tmp & mask) != state) {
+                tmp = (tmp & ~mask) | state;
+                ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
+        }
+
+        return ret;
+}
+
+static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
+{
+        int ret;
+        u8 data[7];
+
+        /* Read first, so we can leave config bits untouched */
+        ret = mcp795_rtcc_read(dev, 0x01, data, sizeof(data));
+
+        if (ret)
+                return ret;
+
+        data[0] = (data[0] & 0x80) | ((tim->tm_sec / 10) << 4) | (tim->tm_sec % 10);
+        data[1] = (data[1] & 0x80) | ((tim->tm_min / 10) << 4) | (tim->tm_min % 10);
+        data[2] = ((tim->tm_hour / 10) << 4) | (tim->tm_hour % 10);
+        data[4] = ((tim->tm_mday / 10) << 4) | ((tim->tm_mday) % 10);
+        data[5] = (data[5] & 0x10) | (tim->tm_mon / 10) | (tim->tm_mon % 10);
+
+        if (tim->tm_year > 100)
+                tim->tm_year -= 100;
+
+        data[6] = ((tim->tm_year / 10) << 4) | (tim->tm_year % 10);
+
+        ret = mcp795_rtcc_write(dev, 0x01, data, sizeof(data));
+
+        if (ret)
+                return ret;
+
+        dev_dbg(dev, "Set mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
+                        tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
+                        tim->tm_hour, tim->tm_min, tim->tm_sec);
+
+        return 0;
+}
+
+static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
+{
+        int ret;
+        u8 data[7];
+
+        ret = mcp795_rtcc_read(dev, 0x01, data, sizeof(data));
+
+        if (ret)
+                return ret;
+
+        tim->tm_sec             = ((data[0] & 0x70) >> 4) * 10 + (data[0] & 0x0f);
+        tim->tm_min             = ((data[1] & 0x70) >> 4) * 10 + (data[1] & 0x0f);
+        tim->tm_hour    = ((data[2] & 0x30) >> 4) * 10 + (data[2] & 0x0f);
+        tim->tm_mday    = ((data[4] & 0x30) >> 4) * 10 + (data[4] & 0x0f);
+        tim->tm_mon             = ((data[5] & 0x10) >> 4) * 10 + (data[5] & 0x0f);
+        tim->tm_year    = ((data[6] & 0xf0) >> 4) * 10 + (data[6] & 0x0f) + 100; /* Assume we are in 20xx */
+
+        dev_dbg(dev, "Read from mcp795: %04d-%02d-%02d %02d:%02d:%02d\n",
+                                tim->tm_year + 1900, tim->tm_mon, tim->tm_mday,
+                                tim->tm_hour, tim->tm_min, tim->tm_sec);
+
+        return rtc_valid_tm(tim);
+}
+
+static struct rtc_class_ops mcp795_rtc_ops = {
+                .read_time = mcp795_read_time,
+                .set_time = mcp795_set_time
+};
+
+static int mcp795_probe(struct spi_device *spi)
+{
+        struct rtc_device *rtc;
+        int ret;
+
+        spi->mode = SPI_MODE_0;
+        spi->bits_per_word = 8;
+        ret = spi_setup(spi);
+        if (ret) {
+                dev_err(&spi->dev, "Unable to setup SPI\n");
+                return ret;
+        }
+
+        /* Start the oscillator */
+        mcp795_rtcc_set_bits(&spi->dev, 0x01, MCP795_ST_BIT, MCP795_ST_BIT);
+        /* Clear the 12 hour mode flag*/
+        mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
+
+        rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
+                                                                &mcp795_rtc_ops, THIS_MODULE);
+        if (IS_ERR(rtc))
+                return PTR_ERR(rtc);
+
+        spi_set_drvdata(spi, rtc);
+
+        return 0;
+}
+
+static struct spi_driver mcp795_driver = {
+                .driver = {
+                                .name = "rtc-mcp795",
+                                .owner = THIS_MODULE,
+                },
+                .probe = mcp795_probe,
+};
+
+module_spi_driver(mcp795_driver);
+
+MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
+MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:mcp795");