[PATCH v3 1/5] fdt: add support for adding pmem nodes

[Heinrich Schuchardt]

On 20.01.25 11:50, Sughosh Ganu wrote:
> From: Masahisa Kojima <kojima.masahisa at socionext.com>
>
> One of the problems OS installers face, when running in EFI, is that
> the mounted ISO after calling ExitBootServices goes away. For some
> distros this is a problem since they rely on finding some core packages
> before continuing the installation. Distros have works around this --
> e.g Fedora has a special kernel command line parameter called
> inst.stage2 [0].
>
> 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 use it when launhing OS installers with EFI.

We also have ACPI support in U-Boot. In a future patch series I guess we
could add the generation of said ACPI tables.

>
> [0]
> https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/installation_guide/chap-anaconda-boot-options#sect-boot-options-installer
>
> Signed-off-by: Masahisa Kojima <kojima.masahisa at socionext.com>
> Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> ---
> Changes since V2:
> * Fix a checkpatch error by putting a blank line after a function
>
>   boot/fdt_support.c    | 40 +++++++++++++++++++++++++++++++++++++++-
>   include/fdt_support.h | 13 +++++++++++++
>   2 files changed, 52 insertions(+), 1 deletion(-)
>
> diff --git a/boot/fdt_support.c b/boot/fdt_support.c
> index 49efeec3681..613685b80eb 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

Do we need this #ifdef at all? We tend to leave it to the linker to
eliminate functions.

>   #if CONFIG_NR_DRAM_BANKS > 4
>   #define MEMORY_BANKS_MAX CONFIG_NR_DRAM_BANKS
>   #else
> @@ -2222,3 +2223,40 @@ int fdt_valid(struct fdt_header **blobp)
>   	}
>   	return 1;
>   }
> +
> +int fdt_fixup_pmem_region(void *blob, ulong addr, u32 size)
> +{
> +	u64 pmem_start[2] = { 0 };
> +	u64 pmem_size[2] = { 0 };
> +	char pmem_node[32] = {0};
> +	int nodeoffset, len;
> +	int err;
> +	u8 tmp[4 * 16]; /* Up to 64-bit address + 64-bit size */
> +
> +	if (!IS_ALIGNED(addr, SZ_2M) || !IS_ALIGNED(addr + size, SZ_2M)) {
> +		printf("Start and end address needs at 2MB alignment\n");

Nits:

%s/needs at 2MB alignment/must be 2 MiB aligned/

> +		return -1;
> +	}
> +	snprintf(pmem_node, sizeof(pmem_node), "pmem@%lx", addr);
> +	nodeoffset = fdt_find_or_add_subnode(blob, 0, pmem_node);
> +	if (nodeoffset < 0)
> +		return nodeoffset;
> +
> +	err = fdt_setprop_string(blob, nodeoffset, "compatible", "pmem-region");
> +	if (err)
> +		return err;
> +	err = fdt_setprop_empty(blob, nodeoffset, "volatile");
> +	if (err)
> +		return err;
> +	pmem_start[0] = addr;
> +	pmem_size[0] = size;
> +	len = fdt_pack_reg(blob, tmp, pmem_start, pmem_size, 1);
> +	err = fdt_setprop(blob, 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..aea24df828f 100644
> --- a/include/fdt_support.h
> +++ b/include/fdt_support.h
> @@ -507,4 +507,17 @@ void fdt_fixup_pstore(void *blob);
>    */
>   int fdt_kaslrseed(void *blob, bool overwrite);
>
> +/**
> + * fdt_fixup_pmem_region() - add a pmem node on the device tree
> + *
> + * This functions injects a pmem node to the device tree. Usually
> + * used with EFI installers to preserve installer images

If I understand the code correctly, the function adds or updates a pmem
device-tree node for the given start address.

Otherwise looks good to me.

Best regards

Heinrich

> + *
> + * @blob:	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 *blob, ulong addr, u32 size);
> +
>   #endif /* ifndef __FDT_SUPPORT_H */