[PATCH v5 2/3] nvmem: add snvs_lpgpr driver

This is a driver for Low Power General Purpose Register (LPGPR)
available on i.MX6 SoCs in Secure Non-Volatile Storage (SNVS)
of this chip.

It is a 32-bit read/write register located in the low power domain.
Since LPGPR is located in the battery-backed power domain, LPGPR can
be used by any application for retaining data during an SoC power-down
mode.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/nvmem/Kconfig      |  10 ++++
 drivers/nvmem/Makefile     |   2 +
 drivers/nvmem/snvs_lpgpr.c | 138 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 150 insertions(+)
 create mode 100644 drivers/nvmem/snvs_lpgpr.c

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 101ced4c84be..ea3044c5d6ee 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig

@@ -144,4 +144,14 @@ config MESON_EFUSE
 	  This driver can also be built as a module. If so, the module
 	  will be called nvmem_meson_efuse.
 
+config NVMEM_SNVS_LPGPR
+	tristate "Support for Low Power General Purpose Register"
+	depends on SOC_IMX6 || COMPILE_TEST
+	help
+	  This is a driver for Low Power General Purpose Register (LPGPR) available on
+	  i.MX6 SoCs in Secure Non-Volatile Storage (SNVS) of this chip.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called nvmem-snvs-lpgpr.
+
 endif

diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 173140658693..4c589184acee 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile

@@ -30,3 +30,5 @@ obj-$(CONFIG_NVMEM_VF610_OCOTP)	+= nvmem-vf610-ocotp.o
 nvmem-vf610-ocotp-y		:= vf610-ocotp.o
 obj-$(CONFIG_MESON_EFUSE)	+= nvmem_meson_efuse.o
 nvmem_meson_efuse-y		:= meson-efuse.o
+obj-$(CONFIG_NVMEM_SNVS_LPGPR)	+= nvmem_snvs_lpgpr.o
+nvmem_snvs_lpgpr-y		:= snvs_lpgpr.o

diff --git a/drivers/nvmem/snvs_lpgpr.c b/drivers/nvmem/snvs_lpgpr.c
new file mode 100644
index 000000000000..acb3ddc0d990
--- /dev/null
+++ b/drivers/nvmem/snvs_lpgpr.c

@@ -0,0 +1,138 @@
+/*
+ * Copyright (c) 2015 Pengutronix, Steffen Trumtrar <kernel@pengutronix.de>
+ * Copyright (c) 2017 Pengutronix, Oleksij Rempel <kernel@pengutronix.de>
+ *
+ * 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/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of_device.h>
+#include <linux/regmap.h>
+
+struct snvs_lpgpr_cfg {
+	int offset;
+};
+
+struct snvs_lpgpr_priv {
+	struct device_d			*dev;
+	struct regmap			*regmap;
+	struct nvmem_config		cfg;
+	const struct snvs_lpgpr_cfg	*dcfg;
+};
+
+static const struct snvs_lpgpr_cfg snvs_lpgpr_cfg_imx6q = {
+	.offset = 0x68,
+};
+
+static int snvs_lpgpr_write(void *context, unsigned int offset, void *_val,
+			    size_t bytes)
+{
+	struct snvs_lpgpr_priv *priv = context;
+	const struct snvs_lpgpr_cfg *dcfg = priv->dcfg;
+	const u32 *val = _val;
+	int i = 0, words = bytes / 4;
+
+	while (words--)
+		regmap_write(priv->regmap, dcfg->offset + offset + (i++ * 4),
+			     *val++);