[PATCH v9 3/8] fdt: add support for adding pmem nodes

[Ilias Apalodimas]

On Mon, 17 Mar 2025 at 10:34, Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
>
> From: Masahisa Kojima <kojima.masahisa at socionext.com>
>
> One of the problems an OS may face, when running in EFI, is that
> a mounted ISO, after calling ExitBootServices goes away, if that ISO
> is resident in RAM memory as a ramdisk.
>
> ACPI has NFIT and NVDIMM support to provide ramdisks to the OS, but we
> don't have anything in place for DTs. Linux and device trees have support
> for persistent memory devices. So add a function that can inject a pmem
> node in a DT, so we can pass information on the ramdisk the OS.
>
> Signed-off-by: Masahisa Kojima <kojima.masahisa at socionext.com>
> Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>


Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>

> ---
> Changes since V8:
> * Re-word the commit message to indicate that the ramdisk information
>   is being passed to the OS through pmem node
> * Change the type of addr and size parameters to the
>   fdt_fixup_pmem_region() as u64
> * Rename the first parameter of fdt_fixup_pmem_region() as fdt instead
>   of blob
> * Modify the format specifier of snprintf() call in
>   fdt_fixup_pmem_region() accordingly
> * Remove pmem_start and pmem_size array variables in
>   fdt_fixup_pmem_region()
> * s/pmem_node/node_name/g
> * Do not initialise node_name variable
>
>  boot/fdt_support.c    | 39 ++++++++++++++++++++++++++++++++++++++-
>  include/fdt_support.h | 14 ++++++++++++++
>  2 files changed, 52 insertions(+), 1 deletion(-)
>
> diff --git a/boot/fdt_support.c b/boot/fdt_support.c
> index 49efeec3681..92f2f534ee0 100644
> --- a/boot/fdt_support.c
> +++ b/boot/fdt_support.c
> @@ -18,6 +18,7 @@
>  #include <dm/ofnode.h>
>  #include <linux/ctype.h>
>  #include <linux/types.h>
> +#include <linux/sizes.h>
>  #include <asm/global_data.h>
>  #include <asm/unaligned.h>
>  #include <linux/libfdt.h>
> @@ -464,7 +465,6 @@ void do_fixup_by_compat_u32(void *fdt, const char *compat,
>         do_fixup_by_compat(fdt, compat, prop, &tmp, 4, create);
>  }
>
> -#ifdef CONFIG_ARCH_FIXUP_FDT_MEMORY
>  /*
>   * fdt_pack_reg - pack address and size array into the "reg"-suitable stream
>   */
> @@ -493,6 +493,7 @@ static int fdt_pack_reg(const void *fdt, void *buf, u64 *address, u64 *size,
>         return p - (char *)buf;
>  }
>
> +#ifdef CONFIG_ARCH_FIXUP_FDT_MEMORY
>  #if CONFIG_NR_DRAM_BANKS > 4
>  #define MEMORY_BANKS_MAX CONFIG_NR_DRAM_BANKS
>  #else
> @@ -2222,3 +2223,39 @@ int fdt_valid(struct fdt_header **blobp)
>         }
>         return 1;
>  }
> +
> +int fdt_fixup_pmem_region(void *fdt, u64 pmem_start, u64 pmem_size)
> +{
> +       char node_name[32];
> +       int nodeoffset, len;
> +       int err;
> +       u8 tmp[4 * 16]; /* Up to 64-bit address + 64-bit size */
> +
> +       if (!IS_ALIGNED(pmem_start, SZ_2M) ||
> +           !IS_ALIGNED(pmem_start + pmem_size, SZ_2M)) {
> +               printf("Start and end address must be 2MiB aligned\n");
> +               return -1;
> +       }
> +
> +       snprintf(node_name, sizeof(node_name), "pmem@%llx", pmem_start);
> +       nodeoffset = fdt_find_or_add_subnode(fdt, 0, node_name);
> +       if (nodeoffset < 0)
> +               return nodeoffset;
> +
> +       err = fdt_setprop_string(fdt, nodeoffset, "compatible", "pmem-region");
> +       if (err)
> +               return err;
> +       err = fdt_setprop_empty(fdt, nodeoffset, "volatile");
> +       if (err)
> +               return err;
> +
> +       len = fdt_pack_reg(fdt, tmp, &pmem_start, &pmem_size, 1);
> +       err = fdt_setprop(fdt, nodeoffset, "reg", tmp, len);
> +       if (err < 0) {
> +               printf("WARNING: could not set pmem %s %s.\n", "reg",
> +                      fdt_strerror(err));
> +               return err;
> +       }
> +
> +       return 0;
> +}
> diff --git a/include/fdt_support.h b/include/fdt_support.h
> index f0ad2e6b365..049190cf3d7 100644
> --- a/include/fdt_support.h
> +++ b/include/fdt_support.h
> @@ -471,6 +471,20 @@ int fdt_valid(struct fdt_header **blobp);
>   */
>  int fdt_get_cells_len(const void *blob, char *nr_cells_name);
>
> +/**
> + * fdt_fixup_pmem_region() - add a pmem node on the device tree
> + *
> + * This functions adds/updates a pmem node to the device tree.
> + * Usually used with EFI installers to preserve installer
> + * images
> + *
> + * @fdt:       device tree provided by caller
> + * @addr:      start address of the pmem node
> + * @size:      size of the memory of the pmem node
> + * Return:     0 on success or < 0 on failure
> + */
> +int fdt_fixup_pmem_region(void *fdt, u64 pmem_start, u64 pmem_size);
> +
>  #endif /* !USE_HOSTCC */
>
>  #ifdef USE_HOSTCC
> --
> 2.34.1
>