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- From 5a3fa75a4d9cb6bcfc9081ef224a4cdcd4b3eafe Mon Sep 17 00:00:00 2001
- From: Nicolas Saenz Julienne <[email protected]>
- Date: Fri, 29 Jan 2021 17:14:29 +0000
- Subject: [PATCH] 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 <[email protected]>
- Reviewed-by: Rob Herring <[email protected]>
- Signed-off-by: Nicolas Saenz Julienne <[email protected]>
- Signed-off-by: Srinivas Kandagatla <[email protected]>
- Link: https://lore.kernel.org/r/[email protected]
- Signed-off-by: Greg Kroah-Hartman <[email protected]>
- ---
- drivers/nvmem/Kconfig | 8 ++++
- drivers/nvmem/Makefile | 2 +
- drivers/nvmem/rmem.c | 97 ++++++++++++++++++++++++++++++++++++++++++
- drivers/of/platform.c | 1 +
- 4 files changed, 108 insertions(+)
- create mode 100644 drivers/nvmem/rmem.c
- --- 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
- --- a/drivers/nvmem/Makefile
- +++ b/drivers/nvmem/Makefile
- @@ -55,3 +55,5 @@ obj-$(CONFIG_NVMEM_ZYNQMP) += nvmem_zynq
- nvmem_zynqmp_nvmem-y := zynqmp_nvmem.o
- obj-$(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
- --- /dev/null
- +++ b/drivers/nvmem/rmem.c
- @@ -0,0 +1,97 @@
- +// SPDX-License-Identifier: GPL-2.0+
- +/*
- + * Copyright (C) 2020 Nicolas Saenz Julienne <[email protected]>
- + */
- +
- +#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 <[email protected]>");
- +MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
- +MODULE_LICENSE("GPL");
- --- a/drivers/of/platform.c
- +++ b/drivers/of/platform.c
- @@ -511,6 +511,7 @@ static const struct of_device_id reserve
- { .compatible = "qcom,rmtfs-mem" },
- { .compatible = "qcom,cmd-db" },
- { .compatible = "ramoops" },
- + { .compatible = "nvmem-rmem" },
- {}
- };
-
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