nvmem: add support for new read-only memory (rmem) binding

Only upstream user of this binding is the raspberry pi 4 DT, where it's
used to pass along bootloader-provided info to Linux. We have instances
in barebox, where a previous stage bootloader passes along a memory
region with info for barebox to interpret. This could in future be
modelled as nvmem-rmem nodes. The binding is also quite handy for
debugging.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20210619034516.6737-4-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

4 files changed, 92 insertions, 4 deletions

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index e4a72b1431..0d7c0b7b9e 100644
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -9,6 +9,12 @@ menuconfig NVMEM
 
 if NVMEM
 
+config NVMEM_RMEM
+	bool "Reserved Memory Based Driver Support"
+	help
+	  This driver maps reserved memory into an nvmem device. It might be
+	  useful to expose information left by firmware in memory.
+
 config NVMEM_SNVS_LPGPR
 	tristate "Freescale SNVS LPGPR support"
 	select MFD_SYSCON
diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index 617e3725a7..6330f3d6e6 100644
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -5,6 +5,8 @@
 obj-$(CONFIG_NVMEM)		+= nvmem_core.o
 nvmem_core-y			:= core.o regmap.o
 
+obj-$(CONFIG_NVMEM_RMEM)	+= rmem.o
+
 # Devices
 obj-$(CONFIG_NVMEM_SNVS_LPGPR)	+= nvmem_snvs_lpgpr.o
 nvmem_snvs_lpgpr-y		:= snvs_lpgpr.o
diff --git a/drivers/nvmem/rmem.c b/drivers/nvmem/rmem.c
new file mode 100644
index 0000000000..e103cec448
--- /dev/null
+++ b/drivers/nvmem/rmem.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
+ */
+
+#include <io.h>
+#include <driver.h>
+#include <linux/nvmem-provider.h>
+#include <init.h>
+
+struct rmem {
+	struct device_d *dev;
+	const struct resource *mem;
+};
+
+static int rmem_read(void *context, unsigned int offset,
+		     void *val, size_t bytes)
+{
+	struct rmem *rmem = context;
+	return mem_copy(rmem->dev, val, (void *)rmem->mem->start + offset,
+			bytes, offset, 0);
+}
+
+static struct nvmem_bus rmem_nvmem_bus = {
+	.read = rmem_read,
+};
+
+static int rmem_probe(struct device_d *dev)
+{
+	struct nvmem_config config = { };
+	struct resource *mem;
+	struct rmem *priv;
+
+	mem = dev_request_mem_resource(dev, 0);
+	if (IS_ERR(mem))
+		return PTR_ERR(mem);
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->mem = mem;
+
+	config.dev = priv->dev = dev;
+	config.priv = priv;
+	config.name = "rmem";
+	config.size = resource_size(mem);
+	config.bus = &rmem_nvmem_bus;
+
+	return PTR_ERR_OR_ZERO(nvmem_register(&config));
+}
+
+static const struct of_device_id rmem_match[] = {
+	{ .compatible = "nvmem-rmem", },
+	{ /* sentinel */ },
+};
+
+static struct driver_d rmem_driver = {
+	.name = "rmem",
+	.of_compatible = rmem_match,
+	.probe = rmem_probe,
+};
+device_platform_driver(rmem_driver);
+
+MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
+MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
+MODULE_LICENSE("GPL");
diff --git a/drivers/of/base.c b/drivers/of/base.c
index 193bae7fa0..015629e1e9 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -2331,9 +2331,14 @@ static void of_platform_device_create_root(struct device_node *np)
 		free(dev);
 }
 
+static const struct of_device_id reserved_mem_matches[] = {
+	{ .compatible = "nvmem-rmem" },
+	{}
+};
+
 int of_probe(void)
 {
-	struct device_node *firmware;
+	struct device_node *node;
 	int ret;
 
 	if(!root_node)
@@ -2347,9 +2352,17 @@ int of_probe(void)
 
 	ret = of_probe_memory();
 
-	firmware = of_find_node_by_path("/firmware");
-	if (firmware)
-		of_platform_populate(firmware, NULL, NULL);
+	/*
+	 * Handle certain compatibles explicitly, since we don't want to create
+	 * platform_devices for every node in /reserved-memory with a
+	 * "compatible",
+	 */
+	for_each_matching_node(node, reserved_mem_matches)
+		of_platform_device_create(node, NULL);
+
+	node = of_find_node_by_path("/firmware");
+	if (node)
+		of_platform_populate(node, NULL, NULL);
 
 	of_platform_device_create_root(root_node);