firmware: bcm47xx_nvram: refactor finding & reading NVRAM

1. Use meaningful variable names (e.g. "flash_start", "res_size" instead
   of e.g. "iobase", "end")
2. Always operate on "offset" instead of mix of start, end, size, etc.
3. Add helper checking for NVRAM to avoid duplicating code
4. Use "found" variable instead of goto
5. Use simpler checking of offsets and sizes (2 nested loops with
   trivial check instead of extra function)

This change has been tested on BCM4706. Updated code checks the same
offsets as before. Driver still finds & copies NVRAM content.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

drivers/firmware/broadcom/bcm47xx_nvram.c

@@ -34,76 +34,91 @@ static char nvram_buf[NVRAM_SPACE];
 static size_t nvram_len;
 static const u32 nvram_sizes[] = {0x6000, 0x8000, 0xF000, 0x10000};
 
-static u32 find_nvram_size(void __iomem *end)
+/**
+ * bcm47xx_nvram_validate - check for a valid NVRAM at specified memory
+ */
+static bool bcm47xx_nvram_is_valid(void __iomem *nvram)
 {
-	struct nvram_header __iomem *header;
-	int i;
+	return ((struct nvram_header *)nvram)->magic == NVRAM_MAGIC;
+}
 
-	for (i = 0; i < ARRAY_SIZE(nvram_sizes); i++) {
-		header = (struct nvram_header *)(end - nvram_sizes[i]);
-		if (header->magic == NVRAM_MAGIC)
-			return nvram_sizes[i];
+/**
+ * bcm47xx_nvram_copy - copy NVRAM to internal buffer
+ */
+static void bcm47xx_nvram_copy(void __iomem *nvram_start, size_t res_size)
+{
+	struct nvram_header __iomem *header = nvram_start;
+	size_t copy_size;
+
+	copy_size = header->len;
+	if (copy_size > res_size) {
+		pr_err("The nvram size according to the header seems to be bigger than the partition on flash\n");
+		copy_size = res_size;
+	}
+	if (copy_size >= NVRAM_SPACE) {
+		pr_err("nvram on flash (%zu bytes) is bigger than the reserved space in memory, will just copy the first %i bytes\n",
+		       copy_size, NVRAM_SPACE - 1);
+		copy_size = NVRAM_SPACE - 1;
 	}
 
-	return 0;
+	__ioread32_copy(nvram_buf, nvram_start, DIV_ROUND_UP(copy_size, 4));
+	nvram_buf[NVRAM_SPACE - 1] = '\0';
+	nvram_len = copy_size;
 }
 
-/* Probe for NVRAM header */
-static int nvram_find_and_copy(void __iomem *iobase, u32 lim)
+/**
+ * bcm47xx_nvram_find_and_copy - find NVRAM on flash mapping & copy it
+ */
+static int bcm47xx_nvram_find_and_copy(void __iomem *flash_start, size_t res_size)
 {
-	struct nvram_header __iomem *header;
-	u32 off;
-	u32 size;
+	size_t flash_size;
+	size_t offset;
+	bool found;
+	int i;
 
 	if (nvram_len) {
 		pr_warn("nvram already initialized\n");
 		return -EEXIST;
 	}
 
 	/* TODO: when nvram is on nand flash check for bad blocks first. */
-	off = FLASH_MIN;
-	while (off <= lim) {
-		/* Windowed flash access */
-		size = find_nvram_size(iobase + off);
-		if (size) {
-			header = (struct nvram_header *)(iobase + off - size);
-			goto found;
+
+	found = false;
+
+	/* Try every possible flash size and check for NVRAM at its end */
+	for (flash_size = FLASH_MIN; flash_size <= res_size; flash_size <<= 1) {
+		for (i = 0; i < ARRAY_SIZE(nvram_sizes); i++) {
+			offset = flash_size - nvram_sizes[i];
+			if (bcm47xx_nvram_is_valid(flash_start + offset)) {
+				found = true;
+				break;
+			}
 		}
-		off <<= 1;
+
+		if (found)
+			break;
 	}
 
 	/* Try embedded NVRAM at 4 KB and 1 KB as last resorts */
-	header = (struct nvram_header *)(iobase + 4096);
-	if (header->magic == NVRAM_MAGIC) {
-		size = NVRAM_SPACE;
-		goto found;
-	}
 
-	header = (struct nvram_header *)(iobase + 1024);
-	if (header->magic == NVRAM_MAGIC) {
-		size = NVRAM_SPACE;
-		goto found;
+	if (!found) {
+		offset = 4096;
+		if (bcm47xx_nvram_is_valid(flash_start + offset))
+			found = true;
 	}
 
-	pr_err("no nvram found\n");
-	return -ENXIO;
-
-found:
-	__ioread32_copy(nvram_buf, header, sizeof(*header) / 4);
-	nvram_len = ((struct nvram_header *)(nvram_buf))->len;
-	if (nvram_len > size) {
-		pr_err("The nvram size according to the header seems to be bigger than the partition on flash\n");
-		nvram_len = size;
+	if (!found) {
+		offset = 1024;
+		if (bcm47xx_nvram_is_valid(flash_start + offset))
+			found = true;
 	}
-	if (nvram_len >= NVRAM_SPACE) {
-		pr_err("nvram on flash (%zu bytes) is bigger than the reserved space in memory, will just copy the first %i bytes\n",
-		       nvram_len, NVRAM_SPACE - 1);
-		nvram_len = NVRAM_SPACE - 1;
+
+	if (!found) {
+		pr_err("no nvram found\n");
+		return -ENXIO;
 	}
-	/* proceed reading data after header */
-	__ioread32_copy(nvram_buf + sizeof(*header), header + 1,
-			DIV_ROUND_UP(nvram_len, 4));
-	nvram_buf[NVRAM_SPACE - 1] = '\0';
+
+	bcm47xx_nvram_copy(flash_start + offset, res_size - offset);
 
 	return 0;
 }
@@ -124,7 +139,7 @@ int bcm47xx_nvram_init_from_mem(u32 base, u32 lim)
 	if (!iobase)
 		return -ENOMEM;
 
-	err = nvram_find_and_copy(iobase, lim);
+	err = bcm47xx_nvram_find_and_copy(iobase, lim);
 
 	iounmap(iobase);