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>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

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

drivers/nvmem/snvs_lpgpr.c

@@ -0,0 +1,156 @@
+/*
+ * 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>
+
+#define IMX6Q_SNVS_HPLR		0x00
+#define IMX6Q_GPR_SL		BIT(5)
+#define IMX6Q_SNVS_LPLR		0x34
+#define IMX6Q_GPR_HL		BIT(5)
+#define IMX6Q_SNVS_LPGPR	0x68
+
+struct snvs_lpgpr_cfg {
+	int offset;
+	int offset_hplr;
+	int offset_lplr;
+};
+
+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		= IMX6Q_SNVS_LPGPR,
+	.offset_hplr	= IMX6Q_SNVS_HPLR,
+	.offset_lplr	= IMX6Q_SNVS_LPLR,
+};
+
+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;
+	unsigned int lock_reg;
+	int ret;
+
+	ret = regmap_read(priv->regmap, dcfg->offset_hplr, &lock_reg);
+	if (ret < 0)
+		return ret;
+
+	if (lock_reg & IMX6Q_GPR_SL)
+		return -EPERM;
+
+	ret = regmap_read(priv->regmap, dcfg->offset_lplr, &lock_reg);
+	if (ret < 0)
+		return ret;
+
+	if (lock_reg & IMX6Q_GPR_HL)
+		return -EPERM;
+
+	return regmap_bulk_write(priv->regmap, dcfg->offset + offset, val,
+				bytes / 4);
+}
+
+static int snvs_lpgpr_read(void *context, unsigned int offset, void *val,
+			   size_t bytes)
+{
+	struct snvs_lpgpr_priv *priv = context;
+	const struct snvs_lpgpr_cfg *dcfg = priv->dcfg;
+
+	return regmap_bulk_read(priv->regmap, dcfg->offset + offset,
+			       val, bytes / 4);
+}
+
+static int snvs_lpgpr_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *node = dev->of_node;
+	struct device_node *syscon_node;
+	struct snvs_lpgpr_priv *priv;
+	struct nvmem_config *cfg;
+	struct nvmem_device *nvmem;
+	const struct snvs_lpgpr_cfg *dcfg;
+
+	if (!node)
+		return -ENOENT;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	dcfg = of_device_get_match_data(dev);
+	if (!dcfg)
+		return -EINVAL;
+
+	syscon_node = of_get_parent(node);
+	if (!syscon_node)
+		return -ENODEV;
+
+	priv->regmap = syscon_node_to_regmap(syscon_node);
+	of_node_put(syscon_node);
+	if (IS_ERR(priv->regmap))
+		return PTR_ERR(priv->regmap);
+
+	priv->dcfg = dcfg;
+
+	cfg = &priv->cfg;
+	cfg->priv = priv;
+	cfg->name = dev_name(dev);
+	cfg->dev = dev;
+	cfg->stride = 4,
+	cfg->word_size = 4,
+	cfg->size = 4,
+	cfg->owner = THIS_MODULE,
+	cfg->reg_read  = snvs_lpgpr_read,
+	cfg->reg_write = snvs_lpgpr_write,
+
+	nvmem = nvmem_register(cfg);
+	if (IS_ERR(nvmem))
+		return PTR_ERR(nvmem);
+
+	platform_set_drvdata(pdev, nvmem);
+
+	return 0;
+}
+
+static int snvs_lpgpr_remove(struct platform_device *pdev)
+{
+	struct nvmem_device *nvmem = platform_get_drvdata(pdev);
+
+	return nvmem_unregister(nvmem);
+}
+
+static const struct of_device_id snvs_lpgpr_dt_ids[] = {
+	{ .compatible = "fsl,imx6q-snvs-lpgpr", .data = &snvs_lpgpr_cfg_imx6q },
+	{ .compatible = "fsl,imx6ul-snvs-lpgpr",
+	  .data = &snvs_lpgpr_cfg_imx6q },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, snvs_lpgpr_dt_ids);
+
+static struct platform_driver snvs_lpgpr_driver = {
+	.probe	= snvs_lpgpr_probe,
+	.remove	= snvs_lpgpr_remove,
+	.driver = {
+		.name	= "snvs_lpgpr",
+		.of_match_table = snvs_lpgpr_dt_ids,
+	},
+};
+module_platform_driver(snvs_lpgpr_driver);
+
+MODULE_AUTHOR("Oleksij Rempel <o.rempel@pengutronix.de>");
+MODULE_DESCRIPTION("Low Power General Purpose Register in i.MX6 Secure Non-Volatile Storage");
+MODULE_LICENSE("GPL v2");