firmware/nvram: bcm47xx: support init from IO memory

Provide NVMEM content to the NVRAM driver from a simple
memory resource. This is necessary to use NVRAM in a memory-
mapped flash device. Patch taken from OpenWrts development
tree.

This patch makes it possible to use memory-mapped NVRAM
on the D-Link DWL-8610AP and the D-Link DIR-890L.

Cc: Hauke Mehrtens <[e-mail]>
Cc: [e-mail]
Cc: Florian Fainelli <[e-mail]>
Cc: [e-mail]
Cc: Thomas Bogendoerfer <[e-mail]>
Signed-off-by: Rafał Miłecki <[e-mail]>
[Added an export for modules potentially using the init symbol]
Signed-off-by: Linus Walleij <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Florian Fainelli <[e-mail]>

drivers/firmware/broadcom/bcm47xx_nvram.c

···
 	return 0;
 }
 
+int bcm47xx_nvram_init_from_iomem(void __iomem *nvram_start, size_t res_size)
+{
+	if (nvram_len) {
+		pr_warn("nvram already initialized\n");
+		return -EEXIST;
+	}
+
+	if (!bcm47xx_nvram_is_valid(nvram_start)) {
+		pr_err("No valid NVRAM found\n");
+		return -ENOENT;
+	}
+
+	bcm47xx_nvram_copy(nvram_start, res_size);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(bcm47xx_nvram_init_from_iomem);
+
 /*
  * On bcm47xx we need access to the NVRAM very early, so we can't use mtd
  * subsystem to access flash. We can't even use platform device / driver to

drivers/nvmem/brcm_nvram.c

···
  * Copyright (C) 2021 Rafał Miłecki <[e-mail]>
  */
 
+#include <linux/bcm47xx_nvram.h>
 #include <linux/io.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
···
 	err = brcm_nvram_parse(priv);
 	if (err)
 		return err;
+
+	bcm47xx_nvram_init_from_iomem(priv->base, resource_size(res));
 
 	config.dev = dev;
 	config.cells = priv->cells;

include/linux/bcm47xx_nvram.h

···
 #include <linux/vmalloc.h>
 
 #ifdef CONFIG_BCM47XX_NVRAM
+int bcm47xx_nvram_init_from_iomem(void __iomem *nvram_start, size_t res_size);
 int bcm47xx_nvram_init_from_mem(u32 base, u32 lim);
 int bcm47xx_nvram_getenv(const char *name, char *val, size_t val_len);
 int bcm47xx_nvram_gpio_pin(const char *name);
···
 	vfree(nvram);
 };
 #else
+static inline int bcm47xx_nvram_init_from_iomem(void __iomem *nvram_start,
+						size_t res_size)
+{
+	return -ENOTSUPP;
+}
 static inline int bcm47xx_nvram_init_from_mem(u32 base, u32 lim)
 {
 	return -ENOTSUPP;