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

From: Masahisa Kojima <kojima.masahisa@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@socionext.com>
Signed-off-by: Sughosh Ganu <sughosh.ganu@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(-)

On Mon, 17 Mar 2025 at 10:34, Sughosh Ganu <sughosh.ganu@linaro.org> wrote:
>
> From: Masahisa Kojima <kojima.masahisa@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@socionext.com>
> Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>


Reviewed-by: Ilias Apalodimas <ilias.apalodimas@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
>