target/linux/bcm27xx/patches-5.10/950-0446-nvmem-Add-driver-to-expose-reserved-memory-as-nvmem.patch

   1 From 639949895123bb937b374ccacae0675ff4ab6e55 Mon Sep 17 00:00:00 2001
   2 From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
   3 Date: Thu, 10 Dec 2020 12:13:49 +0100
   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 Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
  15
  16 ---
  17
  18 Changes since v1:
  19  - Remove reserved memory phandle indirection by directly creating a
  20    platform device from the reserved memory DT node
  21  - Only map memory upon reading it to avoid corruption
  22  - Small cosmetic cleanups
  23 ---
  24  drivers/nvmem/Kconfig  |  8 ++++
  25  drivers/nvmem/Makefile |  2 +
  26  drivers/nvmem/rmem.c   | 97 ++++++++++++++++++++++++++++++++++++++++++
  27  drivers/of/platform.c  |  1 +
  28  4 files changed, 108 insertions(+)
  29  create mode 100644 drivers/nvmem/rmem.c
  30
  31 --- a/drivers/nvmem/Kconfig
  32 +++ b/drivers/nvmem/Kconfig
  33 @@ -270,4 +270,12 @@ config SPRD_EFUSE
  34           This driver can also be built as a module. If so, the module
  35           will be called nvmem-sprd-efuse.
  36
  37 +config NVMEM_RMEM
  38 +       tristate "Reserved Memory Based Driver Support"
  39 +       help
  40 +         This drivers maps reserved memory into an nvmem device. It might be
  41 +         useful to expose information left by firmware in memory.
  42 +
  43 +         This driver can also be built as a module. If so, the module
  44 +         will be called nvmem-rmem.
  45  endif
  46 --- a/drivers/nvmem/Makefile
  47 +++ b/drivers/nvmem/Makefile
  48 @@ -55,3 +55,5 @@ obj-$(CONFIG_NVMEM_ZYNQMP)    += nvmem_zynq
  49  nvmem_zynqmp_nvmem-y           := zynqmp_nvmem.o
  50  obj-$(CONFIG_SPRD_EFUSE)       += nvmem_sprd_efuse.o
  51  nvmem_sprd_efuse-y             := sprd-efuse.o
  52 +obj-$(CONFIG_NVMEM_RMEM)       += nvmem-rmem.o
  53 +nvmem-rmem-y                   := rmem.o
  54 --- /dev/null
  55 +++ b/drivers/nvmem/rmem.c
  56 @@ -0,0 +1,97 @@
  57 +// SPDX-License-Identifier: GPL-2.0+
  58 +/*
  59 + * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
  60 + */
  61 +
  62 +#include <linux/io.h>
  63 +#include <linux/module.h>
  64 +#include <linux/nvmem-provider.h>
  65 +#include <linux/of_reserved_mem.h>
  66 +#include <linux/platform_device.h>
  67 +
  68 +struct rmem {
  69 +       struct device *dev;
  70 +       struct nvmem_device *nvmem;
  71 +       struct reserved_mem *mem;
  72 +
  73 +       phys_addr_t size;
  74 +};
  75 +
  76 +static int rmem_read(void *context, unsigned int offset,
  77 +                    void *val, size_t bytes)
  78 +{
  79 +       struct rmem *priv = context;
  80 +       size_t available = priv->mem->size;
  81 +       loff_t off = offset;
  82 +       void *addr;
  83 +       int count;
  84 +
  85 +       /*
  86 +        * Only map the reserved memory at this point to avoid potential rogue
  87 +        * kernel threads inadvertently modifying it. Based on the current
  88 +        * uses-cases for this driver, the performance hit isn't a concern.
  89 +        * Nor is likely to be, given the nature of the subsystem. Most nvmem
  90 +        * devices operate over slow buses to begin with.
  91 +        *
  92 +        * An alternative would be setting the memory as RO, set_memory_ro(),
  93 +        * but as of Dec 2020 this isn't possible on arm64.
  94 +        */
  95 +       addr = memremap(priv->mem->base, available, MEMREMAP_WB);
  96 +       if (IS_ERR(addr)) {
  97 +               dev_err(priv->dev, "Failed to remap memory region\n");
  98 +               return PTR_ERR(addr);
  99 +       }
 100 +
 101 +       count = memory_read_from_buffer(val, bytes, &off, addr, available);
 102 +
 103 +       memunmap(addr);
 104 +
 105 +       return count;
 106 +}
 107 +
 108 +static int rmem_probe(struct platform_device *pdev)
 109 +{
 110 +       struct nvmem_config config = { };
 111 +       struct device *dev = &pdev->dev;
 112 +       struct reserved_mem *mem;
 113 +       struct rmem *priv;
 114 +
 115 +       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
 116 +       if (!priv)
 117 +               return -ENOMEM;
 118 +       priv->dev = dev;
 119 +
 120 +       mem = of_reserved_mem_lookup(dev->of_node);
 121 +       if (!mem) {
 122 +               dev_err(dev, "Failed to lookup reserved memory\n");
 123 +               return -EINVAL;
 124 +       }
 125 +       priv->mem = mem;
 126 +
 127 +       config.dev = dev;
 128 +       config.priv = priv;
 129 +       config.name = "rmem";
 130 +       config.size = mem->size;
 131 +       config.reg_read = rmem_read;
 132 +
 133 +       return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
 134 +}
 135 +
 136 +static const struct of_device_id rmem_match[] = {
 137 +       { .compatible = "nvmem-rmem", },
 138 +       { /* sentinel */ },
 139 +};
 140 +MODULE_DEVICE_TABLE(of, rmem_match);
 141 +
 142 +static struct platform_driver rmem_driver = {
 143 +       .probe = rmem_probe,
 144 +       .driver = {
 145 +               .name = "rmem",
 146 +               .of_match_table = rmem_match,
 147 +       },
 148 +};
 149 +module_platform_driver(rmem_driver);
 150 +
 151 +MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
 152 +MODULE_DESCRIPTION("Reserved Memory Based nvmem Driver");
 153 +MODULE_LICENSE("GPL");
 154 --- a/drivers/of/platform.c
 155 +++ b/drivers/of/platform.c
 156 @@ -511,6 +511,7 @@ static const struct of_device_id reserve
 157         { .compatible = "qcom,rmtfs-mem" },
 158         { .compatible = "qcom,cmd-db" },
 159         { .compatible = "ramoops" },
 160 +       { .compatible = "nvmem-rmem" },
 161         {}
 162  };
 163