powerpc/nvram: Enable use Generic NVRAM driver for different size chips

Remove the reliance on a staticly defined NVRAM size, allowing
platforms to support NVRAMs with sizes differing from the standard.

A fall back value is provided for platforms not supporting this extension.
Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/nvram.h

@@ -107,6 +107,9 @@ extern void	pmac_xpram_write(int xpaddr, u8 data);
 /* Synchronize NVRAM */
 extern void	nvram_sync(void);
 
+/* Determine NVRAM size */
+extern ssize_t nvram_get_size(void);
+
 /* Normal access to NVRAM */
 extern unsigned char nvram_read_byte(int i);
 extern void nvram_write_byte(unsigned char c, int i);

arch/powerpc/kernel/setup_32.c

@@ -210,6 +210,14 @@ void nvram_write_byte(unsigned char val, int addr)
 }
 EXPORT_SYMBOL(nvram_write_byte);
 
+ssize_t nvram_get_size(void)
+{
+	if (ppc_md.nvram_size)
+		return ppc_md.nvram_size();
+	return -1;
+}
+EXPORT_SYMBOL(nvram_get_size);
+
 void nvram_sync(void)
 {
 	if (ppc_md.nvram_sync)

drivers/char/generic_nvram.c

@@ -2,7 +2,7 @@
  * Generic /dev/nvram driver for architectures providing some
  * "generic" hooks, that is :
  *
- * nvram_read_byte, nvram_write_byte, nvram_sync
+ * nvram_read_byte, nvram_write_byte, nvram_sync, nvram_get_size
  *
  * Note that an additional hook is supported for PowerMac only
  * for getting the nvram "partition" informations
@@ -28,6 +28,8 @@
 
 #define NVRAM_SIZE	8192
 
+static ssize_t nvram_len;
+
 static loff_t nvram_llseek(struct file *file, loff_t offset, int origin)
 {
 	lock_kernel();
@@ -36,7 +38,7 @@ static loff_t nvram_llseek(struct file *file, loff_t offset, int origin)
 		offset += file->f_pos;
 		break;
 	case 2:
-		offset += NVRAM_SIZE;
+		offset += nvram_len;
 		break;
 	}
 	if (offset < 0) {
@@ -56,9 +58,9 @@ static ssize_t read_nvram(struct file *file, char __user *buf,
 
 	if (!access_ok(VERIFY_WRITE, buf, count))
 		return -EFAULT;
-	if (*ppos >= NVRAM_SIZE)
+	if (*ppos >= nvram_len)
 		return 0;
-	for (i = *ppos; count > 0 && i < NVRAM_SIZE; ++i, ++p, --count)
+	for (i = *ppos; count > 0 && i < nvram_len; ++i, ++p, --count)
 		if (__put_user(nvram_read_byte(i), p))
 			return -EFAULT;
 	*ppos = i;
@@ -74,9 +76,9 @@ static ssize_t write_nvram(struct file *file, const char __user *buf,
 
 	if (!access_ok(VERIFY_READ, buf, count))
 		return -EFAULT;
-	if (*ppos >= NVRAM_SIZE)
+	if (*ppos >= nvram_len)
 		return 0;
-	for (i = *ppos; count > 0 && i < NVRAM_SIZE; ++i, ++p, --count) {
+	for (i = *ppos; count > 0 && i < nvram_len; ++i, ++p, --count) {
 		if (__get_user(c, p))
 			return -EFAULT;
 		nvram_write_byte(c, i);
@@ -133,9 +135,20 @@ static struct miscdevice nvram_dev = {
 
 int __init nvram_init(void)
 {
+	int ret = 0;
+
 	printk(KERN_INFO "Generic non-volatile memory driver v%s\n",
 		NVRAM_VERSION);
-	return misc_register(&nvram_dev);
+	ret = misc_register(&nvram_dev);
+	if (ret != 0)
+		goto out;
+
+	nvram_len = nvram_get_size();
+	if (nvram_len < 0)
+		nvram_len = NVRAM_SIZE;
+
+out:
+	return ret;
 }
 
 void __exit nvram_cleanup(void)