drivers: flash: Add support for Atmel AT25 SPI flash variant

The AT25XV021A variant is a flash variant of Atmel's AT25 family
that adds extra protections, requiring additional writes to the
device to program or erase data.

This commit adds a flash driver for AT25XV021A devices instead of
modifying (1) the existing AT45 SPI flash driver or (2) the
existing AT24/25 EEPROM driver because this variant poses
fundamental changes that affect all aspects of the driver.

Notably,
 - AT25XV021A includes a second status register, and the format
	and functions of the existing status register is
	changed from the existing drivers.
 - AT25XV021A requires executing page or chip erase commands
	before writing, making it incompatible with the
	existing AT24/25 EEPROM driver.
 - AT25XV021A adds a software protection layer that requires
	extra writes before executing program or erase commands.

This driver implements flash_erase, but flash_write also
implicitly erases.

Tested writing to and reading/erasing from an AT25XV021A device
across page boundaries with varying lengths (less than and
greater than page size). Tested chip erase functions. Tested
driver initialization from varying initial hardware states.

Signed-off-by: Liam Ogletree <liam.ogletree@cirrus.com>

Author: logletreecrus

drivers/flash/CMakeLists.txt

@@ -68,6 +68,7 @@ zephyr_library_sources_ifdef(CONFIG_SOC_FLASH_SILABS_SIWX91X soc_flash_silabs_si
 zephyr_library_sources_ifdef(CONFIG_SOC_FLASH_SMARTBOND flash_smartbond.c)
 zephyr_library_sources_ifdef(CONFIG_SOC_FLASH_TELINK_B91 soc_flash_b91.c)
 zephyr_library_sources_ifdef(CONFIG_SOC_FLASH_XMC4XXX soc_flash_xmc4xxx.c)
+zephyr_library_sources_ifdef(CONFIG_SPI_FLASH_AT25XV021A spi_flash_at25xv021a.c)
 zephyr_library_sources_ifdef(CONFIG_SPI_FLASH_AT45 spi_flash_at45.c)
 zephyr_library_sources_ifdef(CONFIG_SPI_NOR spi_nor.c)
 # zephyr-keep-sorted-stop

drivers/flash/Kconfig

@@ -166,6 +166,7 @@ config FLASH_INIT_PRIORITY
 # zephyr-keep-sorted-start
 source "drivers/flash/Kconfig.ambiq"
 source "drivers/flash/Kconfig.andes"
+source "drivers/flash/Kconfig.at25xv021a"
 source "drivers/flash/Kconfig.at45"
 source "drivers/flash/Kconfig.b91"
 source "drivers/flash/Kconfig.cadence_nand"

drivers/flash/Kconfig.at25xv021a

@@ -0,0 +1,17 @@
+# Copyright (c) 2025 Cirrus Logic, Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+config SPI_FLASH_AT25XV021A
+	bool "Atmel AT25 SPI flash variant"
+	default y
+	depends on DT_HAS_ATMEL_AT25XV021A_ENABLED
+	select FLASH_HAS_DRIVER_ENABLED
+	select FLASH_HAS_PAGE_LAYOUT
+	select FLASH_HAS_EXPLICIT_ERASE
+	select SPI
+	help
+		Enable support for AT25XV021A SPI flash variants.
+
+		Vendors that have manufactured such variants include:
+		- Renesas Electronics
+		- Adesto Technologies