Re: [PATCH] Add support for the S-35390A RTC chip.

[Andrew Morton <akpm@linux-foundation.org>]

On Thu,  6 Dec 2007 22:10:27 +0000 Byron Bradley <byron.bbradley@gmail.com> wrote:

> This adds basic get/set time support for the Seiko Instruments
> S-35390A. This chip communicates using I2C and is used on the
> QNAP TS-109/TS-209 NAS devices.
> 

A nice looking little driver.

> +static inline char reverse(char x)
> +{
> +	x = ((x >> 1) & 0x55) | ((x << 1) & 0xaa);
> +	x = ((x >> 2) & 0x33) | ((x << 2) & 0xcc);
> +	return (x >> 4) | (x << 4);
> +}

Please take a peek in include/linux/bitrev.h ;)

(I worry about the handling of right-shift-of-negative-values
in your version, too).

Could you review and runtime test this please?

--- a/drivers/rtc/rtc-s35390a.c~rtc-add-support-for-the-s-35390a-rtc-chip-fix
+++ a/drivers/rtc/rtc-s35390a.c
@@ -12,6 +12,7 @@
 #include <linux/module.h>
 #include <linux/rtc.h>
 #include <linux/i2c.h>
+#include <linux/bitrev.h>
 #include <linux/bcd.h>
 
 #define S35390A_CMD_STATUS1	0
@@ -121,13 +122,6 @@ static int s35390a_reg2hr(struct s35390a
 	return hour;
 }
 
-static inline char reverse(char x)
-{
-	x = ((x >> 1) & 0x55) | ((x << 1) & 0xaa);
-	x = ((x >> 2) & 0x33) | ((x << 2) & 0xcc);
-	return (x >> 4) | (x << 4);
-}
-
 static int s35390a_set_datetime(struct i2c_client *client, struct rtc_time *tm)
 {
 	struct s35390a	*s35390a = i2c_get_clientdata(client);
@@ -149,7 +143,7 @@ static int s35390a_set_datetime(struct i
 
 	/* This chip expects the bits of each byte to be in reverse order */
 	for (i = 0; i < 7; ++i)
-		buf[i] = reverse(buf[i]);
+		buf[i] = bitrev8(buf[i]);
 
 	err = s35390a_set_reg(s35390a, S35390A_CMD_TIME1, buf, sizeof(buf));
 
@@ -168,7 +162,7 @@ static int s35390a_get_datetime(struct i
 
 	/* This chip returns the bits of each byte in reverse order */
 	for (i = 0; i < 7; ++i)
-		buf[i] = reverse(buf[i]);
+		buf[i] = bitrev8(buf[i]);
 
 	tm->tm_sec = BCD2BIN(buf[S35390A_BYTE_SECS]);
 	tm->tm_min = BCD2BIN(buf[S35390A_BYTE_MINS]);
_