target/linux/generic/backport-5.10/802-v5.12-0003-nvmem-Add-driver-to-expose-reserved-memory-as-nvmem.patch

   1 From 5a3fa75a4d9cb6bcfc9081ef224a4cdcd4b3eafe Mon Sep 17 00:00:00 2001
   2 From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
   3 Date: Fri, 29 Jan 2021 17:14:29 +0000
   4 Subject: [PATCH] nvmem: Add driver to expose reserved memory as nvmem
   5
   6 Firmware/co-processors might use reserved memory areas in order to pass
   7 data stemming from an nvmem device otherwise non accessible to Linux.
   8 For example an EEPROM memory only physically accessible to firmware, or
   9 data only accessible early at boot time.
  10
  11 In order to expose this data to other drivers and user-space, the driver
  12 models the reserved memory area as an nvmem device.
  13
  14 Tested-by: Tim Gover <tim.gover@raspberrypi.com>
  15 Reviewed-by: Rob Herring <robh@kernel.org>
  16 Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
  17 Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
  18 Link: https://lore.kernel.org/r/20210129171430.11328-5-srinivas.kandagatla@linaro.org
  19 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  20 ---
  21  drivers/nvmem/Kconfig  |  8 ++++
  22  drivers/nvmem/Makefile |  2 +
  23  drivers/nvmem/rmem.c   | 97 ++++++++++++++++++++++++++++++++++++++++++
  24  drivers/of/platform.c  |  1 +
  25  4 files changed, 108 insertions(+)
  26  create mode 100644 drivers/nvmem/rmem.c
  27
  28 --- a/drivers/nvmem/Kconfig
  29 +++ b/drivers/nvmem/Kconfig
  30 @@ -270,4 +270,12 @@ config SPRD_EFUSE
  31           This driver can also be built as a module. If so, the module
  32           will be called nvmem-sprd-efuse.
  33
  34 +config NVMEM_RMEM
  35 +       tristate "Reserved Memory Based Driver Support"
  36 +       help
  37 +         This drivers maps reserved memory into an nvmem device. It might be
  38 +         useful to expose information left by firmware in memory.
  39 +
  40 +         This driver can also be built as a module. If so, the module
  41 +         will be called nvmem-rmem.
  42  endif
  43 --- a/drivers/nvmem/Makefile
  44 +++ b/drivers/nvmem/Makefile
  45 @@ -55,3 +55,5 @@ obj-$(CONFIG_NVMEM_ZYNQMP)    += nvmem_zynq
  46  nvmem_zynqmp_nvmem-y           := zynqmp_nvmem.o
  47  obj-$(CONFIG_SPRD_EFUSE)       += nvmem_sprd_efuse.o
  48  nvmem_sprd_efuse-y             := sprd-efuse.o
  49 +obj-$(CONFIG_NVMEM_RMEM)       += nvmem-rmem.o
  50 +nvmem-rmem-y                   := rmem.o
  51 --- /dev/null
  52 +++ b/drivers/nvmem/rmem.c
  53 @@ -0,0 +1,97 @@
  54 +// SPDX-License-Identifier: GPL-2.0+
  55 +/*
  56 + * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
  57 + */
  58 +
  59 +#include <linux/io.h>
  60 +#include <linux/module.h>
  61 +#include <linux/nvmem-provider.h>
  62 +#include <linux/of_reserved_mem.h>
  63 +#include <linux/platform_device.h>
  64 +
  65 +struct rmem {
  66 +       struct device *dev;
  67 +       struct nvmem_device *nvmem;
  68 +       struct reserved_mem *mem;
  69 +
  70 +       phys_addr_t size;
  71 +};
  72 +
  73 +static int rmem_read(void *context, unsigned int offset,
  74 +                    void *val, size_t bytes)
  75 +{
  76 +       struct rmem *priv = context;
  77 +       size_t available = priv->mem->size;
  78 +       loff_t off = offset;
  79 +       void *addr;
  80 +       int count;
  81 +
  82 +       /*
  83 +        * Only map the reserved memory at this point to avoid potential rogue
  84 +        * kernel threads inadvertently modifying it. Based on the current
  85 +        * uses-cases for this driver, the performance hit isn't a concern.
  86 +        * Nor is likely to be, given the nature of the subsystem. Most nvmem
  87 +        * devices operate over slow buses to begin with.
  88 +        *
  89 +        * An alternative would be setting the memory as RO, set_memory_ro(),
  90 +        * but as of Dec 2020 this isn't possible on arm64.
  91 +        */
  92 +       addr = memremap(priv->mem->base, available, MEMREMAP_WB);
  93 +       if (IS_ERR(addr)) {
  94 +               dev_err(priv->dev, "Failed to remap memory region\n");
  95 +               return PTR_ERR(addr);
  96 +       }
  97 +
  98 +       count = memory_read_from_buffer(val, bytes, &off, addr, available);
  99 +
 100 +       memunmap(addr);
 101 +
 102 +       return count;
 103 +}
 104 +
 105 +static int rmem_probe(struct platform_device *pdev)
 106 +{
 107 +       struct nvmem_config config = { };
 108 +       struct device *dev = &pdev->dev;
 109 +       struct reserved_mem *mem;
 110 +       struct rmem *priv;
 111 +
 112 +       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
 113 +       if (!priv)
 114 +               return -ENOMEM;
 115 +       priv->dev = dev;
 116 +
 117 +       mem = of_reserved_mem_lookup(dev->of_node);
 118 +       if (!mem) {
 119 +               dev_err(dev, "Failed to lookup reserved memory\n");
 120 +               return -EINVAL;
 121 +       }
 122 +       priv->mem = mem;
 123 +
 124 +       config.dev = dev;
 125 +       config.priv = priv;
 126 +       config.name = "rmem";
 127 +       config.size = mem->size;
 128 +       config.reg_read = rmem_read;
 129 +
 130 +       return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
 131 +}
 132 +
 133 +static const struct of_device_id rmem_match[] = {
 134 +       { .compatible = "nvmem-rmem", },
 135 +       { /* sentinel */ },
 136 +};
 137 +MODULE_DEVICE_TABLE(of, rmem_match);
 138 +
 139 +static struct platform_driver rmem_driver = {
 140 +       .probe = rmem_probe,
 141 +       .driver = {
 142 +               .name = "rmem",
 143 +               .of_match_table = rmem_match,
 144 +       },
 145 +};
 146 +module_platform_driver(rmem_driver);
 147 +
 148 +MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
 149 +MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
 150 +MODULE_LICENSE("GPL");
 151 --- a/drivers/of/platform.c
 152 +++ b/drivers/of/platform.c
 153 @@ -511,6 +511,7 @@ static const struct of_device_id reserve
 154         { .compatible = "qcom,rmtfs-mem" },
 155         { .compatible = "qcom,cmd-db" },
 156         { .compatible = "ramoops" },
 157 +       { .compatible = "nvmem-rmem" },
 158         {}
 159  };
 160