nvmem: Add driver to expose reserved memory as nvmem

Firmware/co-processors might use reserved memory areas in order to pass
data stemming from an nvmem device otherwise non accessible to Linux.
For example an EEPROM memory only physically accessible to firmware, or
data only accessible early at boot time.

In order to expose this data to other drivers and user-space, the driver
models the reserved memory area as an nvmem device.

Tested-by: Tim Gover <tim.gover@raspberrypi.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210129171430.11328-5-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
index 954d3b4..fecc19b 100644 (file)
--- a/drivers/nvmem/Kconfig
+++ b/drivers/nvmem/Kconfig
@@ -270,4 +270,12 @@ config SPRD_EFUSE
          This driver can also be built as a module. If so, the module
          will be called nvmem-sprd-efuse.
 
+config NVMEM_RMEM
+       tristate "Reserved Memory Based Driver Support"
+       help
+         This drivers maps reserved memory into an nvmem device. It might be
+         useful to expose information left by firmware in memory.
+
+         This driver can also be built as a module. If so, the module
+         will be called nvmem-rmem.
 endif

diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
index a7c3772..5376b8e 100644 (file)
--- a/drivers/nvmem/Makefile
+++ b/drivers/nvmem/Makefile
@@ -55,3 +55,5 @@ obj-$(CONFIG_NVMEM_ZYNQMP)    += nvmem_zynqmp_nvmem.o
 nvmem_zynqmp_nvmem-y           := zynqmp_nvmem.o
 obj-$(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

diff --git a/drivers/nvmem/rmem.c b/drivers/nvmem/rmem.c
new file mode 100644 (file)
index 0000000..b11c3c9
--- /dev/null
+++ b/drivers/nvmem/rmem.c
@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
+ */
+
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of_reserved_mem.h>
+#include <linux/platform_device.h>
+
+struct rmem {
+       struct device *dev;
+       struct nvmem_device *nvmem;
+       struct reserved_mem *mem;
+
+       phys_addr_t size;
+};
+
+static int rmem_read(void *context, unsigned int offset,
+                    void *val, size_t bytes)
+{
+       struct rmem *priv = context;
+       size_t available = priv->mem->size;
+       loff_t off = offset;
+       void *addr;
+       int count;
+
+       /*
+        * Only map the reserved memory at this point to avoid potential rogue
+        * kernel threads inadvertently modifying it. Based on the current
+        * uses-cases for this driver, the performance hit isn't a concern.
+        * Nor is likely to be, given the nature of the subsystem. Most nvmem
+        * devices operate over slow buses to begin with.
+        *
+        * An alternative would be setting the memory as RO, set_memory_ro(),
+        * but as of Dec 2020 this isn't possible on arm64.
+        */
+       addr = memremap(priv->mem->base, available, MEMREMAP_WB);
+       if (IS_ERR(addr)) {
+               dev_err(priv->dev, "Failed to remap memory region\n");
+               return PTR_ERR(addr);
+       }
+
+       count = memory_read_from_buffer(val, bytes, &off, addr, available);
+
+       memunmap(addr);
+
+       return count;
+}
+
+static int rmem_probe(struct platform_device *pdev)
+{
+       struct nvmem_config config = { };
+       struct device *dev = &pdev->dev;
+       struct reserved_mem *mem;
+       struct rmem *priv;
+
+       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+       if (!priv)
+               return -ENOMEM;
+       priv->dev = dev;
+
+       mem = of_reserved_mem_lookup(dev->of_node);
+       if (!mem) {
+               dev_err(dev, "Failed to lookup reserved memory\n");
+               return -EINVAL;
+       }
+       priv->mem = mem;
+
+       config.dev = dev;
+       config.priv = priv;
+       config.name = "rmem";
+       config.size = mem->size;
+       config.reg_read = rmem_read;
+
+       return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
+}
+
+static const struct of_device_id rmem_match[] = {
+       { .compatible = "nvmem-rmem", },
+       { /* sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, rmem_match);
+
+static struct platform_driver rmem_driver = {
+       .probe = rmem_probe,
+       .driver = {
+               .name = "rmem",
+               .of_match_table = rmem_match,
+       },
+};
+module_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/platform.c b/drivers/of/platform.c
index 79bd5f5..6699cdb 100644 (file)
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -511,6 +511,7 @@ static const struct of_device_id reserved_mem_matches[] = {
        { .compatible = "qcom,rmtfs-mem" },
        { .compatible = "qcom,cmd-db" },
        { .compatible = "ramoops" },
+       { .compatible = "nvmem-rmem" },
        {}
 };