[PATCH v8 4/4] efi_vars: Implement SPI Flash store
Heinrich Schuchardt
xypron.glpk at gmx.de
Sun Feb 15 22:55:30 CET 2026
Am 15. Februar 2026 09:48:39 MEZ schrieb Heinrich Schuchardt <xypron.glpk at gmx.de>:
>On 2/11/26 16:56, Michal Simek wrote:
>> From: Shantur Rathore <i at shantur.com>
>>
>> Currently U-Boot uses ESP as storage for EFI variables.
>> Devices with SPI Flash are used for storing environment with this
>> commit we allow EFI variables to be stored on SPI Flash.
>>
>> https://github.com/rhboot/efivar
>> is not updated to support this location that's why you can mimic it by
>> running:
>> dd if=/sys/firmware/efi/efivars/VarToFile-b2ac5fc9-92b7-4acd-aeac-11e818c3130c \
>> of=/tmp/vars skip=4 bs=1
>> flashcp /tmp/vars /dev/mtdX
>>
>> where mtdX should match location defined by
>> CONFIG_EFI_VARIABLE_SF_OFFSET/CONFIG_EFI_VAR_BUF_SIZE.
>>
>> Signed-off-by: Shantur Rathore <i at shantur.com>
>> Signed-off-by: Michal Simek <michal.simek at amd.com>
>> Tested-by: Neil Armstrong <neil.armstrong at linaro.org> # on AML-S905D3-CC
>> Acked-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
>>
>> ---
>>
>> Changes in v8:
>> - Add missing EFI_VARIABLE_SF_STORE dependency to EFI_VARIABLE_SF_DEVICE_INDEX
>>
>> Changes in v7:
>> - sed -i 's/efi_var_from/efi_var_from_storage/g'
>>
>> Changes in v6:
>> - sed -i 's/efi_var_read/efi_var_from/g'
>> - sed -i 's/efi_var_write/efi_var_to_storage/g'
>>
>> Changes in v4:
>> - Extend Kconfig description
>> - Extend commit message and describe efivar missing part
>> - use unify methods for reading/writing variable
>>
>> Changes in v3:
>> - Fixed compiler warnings.
>>
>> Changes in v2:
>> - Refactored efi_var_file to move common parts out as requested
>> - Changed ifdefs to use CONFIG_IS_DEFINED
>> - Fixed typos
>>
>> lib/efi_loader/Kconfig | 35 +++++++++++++-
>> lib/efi_loader/Makefile | 1 +
>> lib/efi_loader/efi_var_sf.c | 92 +++++++++++++++++++++++++++++++++++++
>> 3 files changed, 127 insertions(+), 1 deletion(-)
>> create mode 100644 lib/efi_loader/efi_var_sf.c
>>
>> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
>> index 579eed658801..0f6f927ddaf1 100644
>> --- a/lib/efi_loader/Kconfig
>> +++ b/lib/efi_loader/Kconfig
>> @@ -124,6 +124,24 @@ config EFI_VARIABLE_FILE_STORE
>> Select this option if you want non-volatile UEFI variables to be
>> stored as file /ubootefi.var on the EFI system partition.
>> +config EFI_VARIABLE_SF_STORE
>> + bool "Store non-volatile UEFI variables in SPI Flash"
>> + depends on SPI_FLASH
>> + help
>> + Select this option if you want non-volatile UEFI variables to be
>> + stored in SPI Flash.
>> +
>> + Define CONFIG_EFI_VARIABLE_SF_OFFSET as offset in SPI Flash to use as
>> + the storage for variables. CONFIG_EFI_VAR_BUF_SIZE defines the space
>> + needed.
>> +
>> + Note that SPI Flash devices have a limited number of program/erase
>> + cycles. Frequent updates to UEFI variables may cause excessive wear
>> + and can permanently damage the flash device, particularly on SPI NAND
>> + or low-end SPI NOR parts without wear leveling. This option should be
>> + used with care on such systems, and is not recommended for platforms
>> + where UEFI variables are updated frequently.
>> +
>> config EFI_MM_COMM_TEE
>> bool "UEFI variables storage service via the trusted world"
>> depends on OPTEE
>> @@ -153,7 +171,7 @@ endchoice
>> config EFI_RT_VOLATILE_STORE
>> bool "Allow variable runtime services in volatile storage (e.g RAM)"
>> - depends on EFI_VARIABLE_FILE_STORE
>> + depends on EFI_VARIABLE_FILE_STORE || EFI_VARIABLE_SF_STORE
>
>Hello Michal,
>
>If the backend store is SPI flash, we should not publish the variable "RTStorageVolatile" at runtime as currently defined.
>
>For the background see this commit for the efivar library:
>
>https://github.com/rhboot/efivar/commit/68daa04654acbe1bbaa17ebfc23c371b39e69c6b
>
>The first three patches look correct to me and I will add them to a merge request for efi-next.
The 3 prerequisite patches are now in origin/next. Just this one left to be reworked.
Best regards
Heinrich
>
>The usage of efi_var_mem_ins() and efi_var_mem_del() when SetVariable() does not change anything is not flash-friendly. Michal, do you want to have a look at this area?
>
>@Ilias, @Vincent:
>We currently lack documentation for the 3 variables.
>Would it make sense to add the definition of the variables to chapter source/chapter5-variable-storage.rst.
>
>Would an efivar helper for SPI flash make sense?
>How should RTStorageVolatile describe a SPI flash location?
>
>Best regards
>
>Heinrich
>
>> help
>> When EFI variables are stored on file we don't allow SetVariableRT,
>> since the OS doesn't know how to write that file. At the same time
>> @@ -194,6 +212,21 @@ config FFA_SHARED_MM_BUF_ADDR
>> the MM SP in secure world.
>> It is assumed that the MM SP knows the address of the shared MM communication buffer.
>> +config EFI_VARIABLE_SF_OFFSET
>> + hex "EFI variables in SPI flash offset"
>> + depends on EFI_VARIABLE_SF_STORE
>> + help
>> + Offset from the start of the SPI Flash where EFI variables will be stored.
>> + This should be aligned to the sector size of SPI Flash.
>> +
>> +config EFI_VARIABLE_SF_DEVICE_INDEX
>> + int "Device Index for target SPI Flash"
>> + depends on EFI_VARIABLE_SF_STORE
>> + default 0
>> + help
>> + The index of SPI Flash device used for storing EFI variables. This would be
>> + needed if there are more than 1 SPI Flash devices available to use.
>> +
>> config EFI_VARIABLES_PRESEED
>> bool "Initial values for UEFI variables"
>> depends on !COMPILE_TEST
>> diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
>> index ca1775eb03be..d73ad43951b1 100644
>> --- a/lib/efi_loader/Makefile
>> +++ b/lib/efi_loader/Makefile
>> @@ -54,6 +54,7 @@ obj-y += efi_variable_tee.o
>> else
>> obj-y += efi_variable.o
>> obj-$(CONFIG_EFI_VARIABLE_FILE_STORE) += efi_var_file.o
>> +obj-$(CONFIG_EFI_VARIABLE_SF_STORE) += efi_var_sf.o
>> obj-$(CONFIG_EFI_VARIABLES_PRESEED) += efi_var_seed.o
>> endif
>> obj-y += efi_watchdog.o
>> diff --git a/lib/efi_loader/efi_var_sf.c b/lib/efi_loader/efi_var_sf.c
>> new file mode 100644
>> index 000000000000..61d68f7c5c94
>> --- /dev/null
>> +++ b/lib/efi_loader/efi_var_sf.c
>> @@ -0,0 +1,92 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * SPI Flash interface for UEFI variables
>> + *
>> + * Copyright (c) 2023, Shantur Rathore
>> + * Copyright (C) 2026, Advanced Micro Devices, Inc.
>> + */
>> +
>> +#define LOG_CATEGORY LOGC_EFI
>> +
>> +#include <efi_loader.h>
>> +#include <efi_variable.h>
>> +#include <spi_flash.h>
>> +#include <dm.h>
>> +
>> +efi_status_t efi_var_to_storage(void)
>> +{
>> + efi_status_t ret;
>> + struct efi_var_file *buf;
>> + loff_t len;
>> + struct udevice *sfdev;
>> +
>> + ret = efi_var_collect(&buf, &len, EFI_VARIABLE_NON_VOLATILE);
>> + if (len > EFI_VAR_BUF_SIZE) {
>> + log_err("EFI var buffer length more than target SPI Flash size");
>> + ret = EFI_OUT_OF_RESOURCES;
>> + goto error;
>> + }
>> +
>> + log_debug("%s - Got buffer to write buf->len : %d\n", __func__, buf->length);
>> +
>> + if (ret != EFI_SUCCESS)
>> + goto error;
>> +
>> + ret = uclass_get_device(UCLASS_SPI_FLASH, CONFIG_EFI_VARIABLE_SF_DEVICE_INDEX, &sfdev);
>> + if (ret)
>> + goto error;
>> +
>> + ret = spi_flash_erase_dm(sfdev, CONFIG_EFI_VARIABLE_SF_OFFSET, EFI_VAR_BUF_SIZE);
>> + log_debug("%s - Erased SPI Flash offset %x\n", __func__, CONFIG_EFI_VARIABLE_SF_OFFSET);
>> + if (ret)
>> + goto error;
>> +
>> + ret = spi_flash_write_dm(sfdev, CONFIG_EFI_VARIABLE_SF_OFFSET, len, buf);
>> + log_debug("%s - Wrote buffer to SPI Flash : %ld\n", __func__, ret);
>> +
>> + if (ret)
>> + goto error;
>> +
>> + ret = EFI_SUCCESS;
>> +error:
>> + if (ret)
>> + log_err("Failed to persist EFI variables in SF\n");
>> + free(buf);
>> + return ret;
>> +}
>> +
>> +efi_status_t efi_var_from_storage(void)
>> +{
>> + struct efi_var_file *buf;
>> + efi_status_t ret;
>> + struct udevice *sfdev;
>> +
>> + buf = calloc(1, EFI_VAR_BUF_SIZE);
>> + if (!buf) {
>> + log_err("%s - Unable to allocate buffer\n", __func__);
>> + return EFI_OUT_OF_RESOURCES;
>> + }
>> +
>> + ret = uclass_get_device(UCLASS_SPI_FLASH, 0, &sfdev);
>> + if (ret)
>> + goto error;
>> +
>> + ret = spi_flash_read_dm(sfdev, CONFIG_EFI_VARIABLE_SF_OFFSET,
>> + EFI_VAR_BUF_SIZE, buf);
>> +
>> + log_debug("%s - read buffer buf->length: %x\n", __func__, buf->length);
>> +
>> + if (ret || buf->length < sizeof(struct efi_var_file)) {
>> + log_err("%s - buffer read from SPI Flash isn't valid\n", __func__);
>> + goto error;
>> + }
>> +
>> + ret = efi_var_restore(buf, false);
>> + if (ret != EFI_SUCCESS)
>> + log_err("%s - Unable to restore EFI variables from buffer\n", __func__);
>> +
>> + ret = EFI_SUCCESS;
>> +error:
>> + free(buf);
>> + return ret;
>> +}
>
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