[PATCH 2/2] nvmem: add generic driver for devices with I/O based access

["Rafał Miłecki" <zajec5@gmail.com>]

From: Rafał Miłecki <rafal@milecki.pl>

With nvmem layouts in place we should now work on plain content access
NVMEM drivers (e.g. IO one). Actual NVMEM content handling should go to
layout drivers.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
 drivers/nvmem/Kconfig  |  7 ++++
 drivers/nvmem/Makefile |  2 ++
 drivers/nvmem/io.c     | 79 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 88 insertions(+)
 create mode 100644 drivers/nvmem/io.c

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 789729ff7e50..e77bfe6eb52e 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -90,6 +90,13 @@ config NVMEM_IMX_OCOTP_SCU
 	  This is a driver for the SCU On-Chip OTP Controller (OCOTP)
 	  available on i.MX8 SoCs.
 
+config NVMEM_IO
+	tristate "IO access based NVMEM support"
+	depends on HAS_IOMEM
+	help
+	  This driver provides support for NVMEM devices that can be accessed
+	  using I/O mapping.
+
 config NVMEM_JZ4780_EFUSE
 	tristate "JZ4780 EFUSE Memory Support"
 	depends on MACH_INGENIC || COMPILE_TEST
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 442f9a4876a5..82db0a89c4d6 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -20,6 +20,8 @@ obj-$(CONFIG_NVMEM_IMX_OCOTP)		+= nvmem-imx-ocotp.o
 nvmem-imx-ocotp-y			:= imx-ocotp.o
 obj-$(CONFIG_NVMEM_IMX_OCOTP_SCU)	+= nvmem-imx-ocotp-scu.o
 nvmem-imx-ocotp-scu-y			:= imx-ocotp-scu.o
+obj-$(CONFIG_NVMEM_IO)			+= nvmem-io.o
+nvmem-io-y				:= io.o
 obj-$(CONFIG_NVMEM_JZ4780_EFUSE)	+= nvmem_jz4780_efuse.o
 nvmem_jz4780_efuse-y			:= jz4780-efuse.o
 obj-$(CONFIG_NVMEM_LAN9662_OTPC)	+= nvmem-lan9662-otpc.o
diff --git a/drivers/nvmem/io.c b/drivers/nvmem/io.c
new file mode 100644
index 000000000000..307526fda036
--- /dev/null
+++ b/drivers/nvmem/io.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 Rafał Miłecki <rafal@milecki.pl>
+ */
+
+#include <linux/io.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+struct io_nvmem {
+	void __iomem *base;
+};
+
+static int io_nvmem_read(void *context, unsigned int offset, void *val, size_t bytes)
+{
+	struct io_nvmem *priv = context;
+	u8 *dst = val;
+
+	while (bytes--)
+		*dst++ = readb(priv->base + offset++);
+
+	return 0;
+}
+
+static int io_nvmem_probe(struct platform_device *pdev)
+{
+	struct nvmem_config config = {
+		.name = "io-nvmem",
+		.reg_read = io_nvmem_read,
+	};
+	struct device *dev = &pdev->dev;
+	struct resource *res;
+	struct io_nvmem *priv;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	config.dev = dev;
+	config.priv = priv;
+	config.size = resource_size(res);
+
+	if (!device_property_present(dev, "read-only"))
+		dev_warn(dev, "Writing is not supported yet");
+
+	return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
+}
+
+static const struct of_device_id io_nvmem_of_match_table[] = {
+	{ .compatible = "io-nvmem", },
+	{},
+};
+
+static struct platform_driver io_nvmem_driver = {
+	.probe = io_nvmem_probe,
+	.driver = {
+		.name = "io_nvmem",
+		.of_match_table = io_nvmem_of_match_table,
+	},
+};
+
+static int __init io_nvmem_init(void)
+{
+	return platform_driver_register(&io_nvmem_driver);
+}
+
+subsys_initcall_sync(io_nvmem_init);
+
+MODULE_AUTHOR("Rafał Miłecki");
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(of, io_nvmem_of_match_table);
-- 
2.34.1