[RFC v2 04/24] m68k/atari: Replace nvram_{read,write}_byte with arch_nvram_ops

[Finn Thain <fthain@telegraphics.com.au>]

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By implementing an arch_nvram_ops struct, any platform can re-use the
drivers/char/nvram module without needing any arch-specific code
in that module. Atari does so here.

Atari has one user of nvram_check_checksum() whereas the other platforms
(i.e. x86 and ARM platforms) have none at all. Replace this
validate-checksum-and-read-byte sequence with the equivalent
rtc_nvram_ops.read() call and remove the now unused functions.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>

---

The advantage of the new ops struct over the old global nvram_* functions
is that the misc device module can be shared by different platforms
without requiring every platform to implement every nvram_* function.
E.g. only RTC "CMOS" NVRAMs have a checksum and only PowerPC platforms
have a "sync" ioctl.

---
 arch/m68k/atari/nvram.c   |   89 ++++++++++++++++++++++++++++------------------
 drivers/scsi/atari_scsi.c |    8 ++--
 include/linux/nvram.h     |    9 ++++
 3 files changed, 70 insertions(+), 36 deletions(-)

Index: linux/arch/m68k/atari/nvram.c
===================================================================
--- linux.orig/arch/m68k/atari/nvram.c	2015-06-14 17:45:37.000000000 +1000
+++ linux/arch/m68k/atari/nvram.c	2015-06-14 17:45:39.000000000 +1000
@@ -38,33 +38,12 @@ unsigned char __nvram_read_byte(int i)
 	return CMOS_READ(NVRAM_FIRST_BYTE + i);
 }
 
-unsigned char nvram_read_byte(int i)
-{
-	unsigned long flags;
-	unsigned char c;
-
-	spin_lock_irqsave(&rtc_lock, flags);
-	c = __nvram_read_byte(i);
-	spin_unlock_irqrestore(&rtc_lock, flags);
-	return c;
-}
-EXPORT_SYMBOL(nvram_read_byte);
-
 /* This races nicely with trying to read with checksum checking */
 void __nvram_write_byte(unsigned char c, int i)
 {
 	CMOS_WRITE(c, NVRAM_FIRST_BYTE + i);
 }
 
-void nvram_write_byte(unsigned char c, int i)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&rtc_lock, flags);
-	__nvram_write_byte(c, i);
-	spin_unlock_irqrestore(&rtc_lock, flags);
-}
-
 /* On Ataris, the checksum is over all bytes except the checksum bytes
  * themselves; these are at the very end.
  */
@@ -83,18 +62,6 @@ int __nvram_check_checksum(void)
 	       (__nvram_read_byte(ATARI_CKS_LOC + 1) == (sum & 0xff));
 }
 
-int nvram_check_checksum(void)
-{
-	unsigned long flags;
-	int rv;
-
-	spin_lock_irqsave(&rtc_lock, flags);
-	rv = __nvram_check_checksum();
-	spin_unlock_irqrestore(&rtc_lock, flags);
-	return rv;
-}
-EXPORT_SYMBOL(nvram_check_checksum);
-
 static void __nvram_set_checksum(void)
 {
 	int i;
@@ -106,6 +73,62 @@ static void __nvram_set_checksum(void)
 	__nvram_write_byte(sum, ATARI_CKS_LOC + 1);
 }
 
+static ssize_t nvram_read(char *buf, size_t count, loff_t *ppos)
+{
+	char *p = buf;
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+
+	if (!__nvram_check_checksum()) {
+		spin_unlock_irq(&rtc_lock);
+		return -EIO;
+	}
+
+	for (i = *ppos; count > 0 && i < NVRAM_BYTES; --count, ++i, ++p)
+		*p = __nvram_read_byte(i);
+
+	spin_unlock_irq(&rtc_lock);
+
+	*ppos = i;
+	return p - buf;
+}
+
+static ssize_t nvram_write(char *buf, size_t count, loff_t *ppos)
+{
+	char *p = buf;
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+
+	if (!__nvram_check_checksum()) {
+		spin_unlock_irq(&rtc_lock);
+		return -EIO;
+	}
+
+	for (i = *ppos; count > 0 && i < NVRAM_BYTES; --count, ++i, ++p)
+		__nvram_write_byte(*p, i);
+
+	__nvram_set_checksum();
+
+	spin_unlock_irq(&rtc_lock);
+
+	*ppos = i;
+	return p - buf;
+}
+
+static ssize_t nvram_get_size(void)
+{
+	return NVRAM_BYTES;
+}
+
+const struct nvram_ops arch_nvram_ops = {
+	.read           = nvram_read,
+	.write          = nvram_write,
+	.get_size       = nvram_get_size,
+};
+EXPORT_SYMBOL(arch_nvram_ops);
+
 #ifdef CONFIG_PROC_FS
 static struct {
 	unsigned char val;
Index: linux/drivers/scsi/atari_scsi.c
===================================================================
--- linux.orig/drivers/scsi/atari_scsi.c	2015-06-14 17:45:35.000000000 +1000
+++ linux/drivers/scsi/atari_scsi.c	2015-06-14 17:45:39.000000000 +1000
@@ -880,13 +880,15 @@ static int __init atari_scsi_probe(struc
 #ifdef CONFIG_NVRAM
 	else
 		/* Test if a host id is set in the NVRam */
-		if (ATARIHW_PRESENT(TT_CLK) && nvram_check_checksum()) {
-			unsigned char b = nvram_read_byte(14);
+		if (ATARIHW_PRESENT(TT_CLK)) {
+			unsigned char b;
+			loff_t offset = 14;
+			ssize_t count = arch_nvram_ops.read(&b, 1, &offset);
 
 			/* Arbitration enabled? (for TOS)
 			 * If yes, use configured host ID
 			 */
-			if (b & 0x80)
+			if ((count == 1) && (b & 0x80))
 				atari_scsi_template.this_id = b & 7;
 		}
 #endif
Index: linux/include/linux/nvram.h
===================================================================
--- linux.orig/include/linux/nvram.h	2015-06-14 17:45:34.000000000 +1000
+++ linux/include/linux/nvram.h	2015-06-14 17:45:39.000000000 +1000
@@ -10,4 +10,13 @@ extern void __nvram_write_byte(unsigned
 extern void nvram_write_byte(unsigned char c, int i);
 extern int __nvram_check_checksum(void);
 extern int nvram_check_checksum(void);
+
+struct nvram_ops {
+	ssize_t         (*read)(char *, size_t, loff_t *);
+	ssize_t         (*write)(char *, size_t, loff_t *);
+	ssize_t         (*get_size)(void);
+};
+
+extern const struct nvram_ops arch_nvram_ops;
+
 #endif  /* _LINUX_NVRAM_H */