[PATCH 2/2] nvmem: iomap: new driver exposing NVMEM accessible using I/O mapping

["Rafał Miłecki" <zajec5@gmail.com>]

From: Rafał Miłecki <rafal@milecki.pl>

This is a generic NVMEM access method used e.g. by Broadcom for their
NVRAM on MIPS and Northstar devices.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
 drivers/nvmem/Kconfig  |  7 +++
 drivers/nvmem/Makefile |  2 +
 drivers/nvmem/iomap.c  | 99 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 108 insertions(+)
 create mode 100644 drivers/nvmem/iomap.c

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 75d2594c16e1..3d5c5684685d 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -278,4 +278,11 @@ config NVMEM_RMEM
 
 	  This driver can also be built as a module. If so, the module
 	  will be called nvmem-rmem.
+
+config NVMEM_IOMAP
+	tristate "I/O mapped NVMEM support"
+	depends on HAS_IOMEM
+	help
+	  This driver supports NVMEM that can be accessed using I/O mapping.
+
 endif
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 5376b8e0dae5..88a3b6979c53 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -57,3 +57,5 @@ obj-$(CONFIG_SPRD_EFUSE)	+= nvmem_sprd_efuse.o
 nvmem_sprd_efuse-y		:= sprd-efuse.o
 obj-$(CONFIG_NVMEM_RMEM) 	+= nvmem-rmem.o
 nvmem-rmem-y			:= rmem.o
+obj-$(CONFIG_NVMEM_IOMAP)	+= nvmem_iomap.o
+nvmem_iomap-y			:= iomap.o
diff --git a/drivers/nvmem/iomap.c b/drivers/nvmem/iomap.c
new file mode 100644
index 000000000000..ab6b40858a64
--- /dev/null
+++ b/drivers/nvmem/iomap.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 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>
+
+struct iomap {
+	struct device *dev;
+	void __iomem *base;
+};
+
+static int iomap_read(void *context, unsigned int offset, void *val,
+		      size_t bytes)
+{
+	struct iomap *priv = context;
+	u8 *src = priv->base + offset;
+	u8 *dst = val;
+	size_t tmp;
+
+	tmp = offset % 4;
+	memcpy_fromio(dst, src, tmp);
+	dst += tmp;
+	src += tmp;
+	bytes -= tmp;
+
+	tmp = rounddown(bytes, 4);
+	__ioread32_copy(dst, src, tmp / 4);
+	dst += tmp;
+	src += tmp;
+	bytes -= tmp;
+
+	memcpy_fromio(dst, src, bytes);
+
+	return 0;
+}
+
+static int iomap_probe(struct platform_device *pdev)
+{
+	struct nvmem_config config = {
+		.name = "iomap",
+		.reg_read = iomap_read,
+	};
+	struct device *dev = &pdev->dev;
+	struct resource *res;
+	struct iomap *priv;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+	priv->dev = dev;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res) {
+		dev_err(dev, "Failed to get resource\n");
+		return -ENODEV;
+	}
+
+	priv->base = devm_ioremap_resource(dev, res);
+	if (IS_ERR(priv->base)) {
+		dev_err(dev, "Failed to map resource: %ld\n", PTR_ERR(priv->base));
+		return PTR_ERR(priv->base);
+	}
+
+	config.dev = dev;
+	config.priv = priv;
+	config.size = resource_size(res);
+
+	return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
+}
+
+static const struct of_device_id iomap_of_match_table[] = {
+	{ .compatible = "brcm,nvram", },
+	{ .compatible = "nvmem-iomap", },
+	{},
+};
+
+static struct platform_driver iomap_driver = {
+	.probe = iomap_probe,
+	.driver = {
+		.name = "nvmem_iomap",
+		.of_match_table = iomap_of_match_table,
+	},
+};
+
+static int __init iomap_init(void)
+{
+	return platform_driver_register(&iomap_driver);
+}
+
+subsys_initcall_sync(iomap_init);
+
+MODULE_AUTHOR("Rafał Miłecki");
+MODULE_LICENSE("GPL v2");
+MODULE_DEVICE_TABLE(of, iomap_of_match_table);
-- 
2.26.2