[PATCH 1/5 v2] cx22702: Clean up register access functions

[Jean Delvare <khali@linux-fr.org>]

Hi Mauro,

On Fri, 10 Sep 2010 12:13:32 -0300, Mauro Carvalho Chehab wrote:
> Em 10-09-2010 10:27, Jean Delvare escreveu:
> > * Avoid temporary variables.
> > * Optimize success paths.
> > * Make error messages consistently verbose.
> > 
> > Signed-off-by: Jean Delvare <khali@linux-fr.org>
> > Cc: Steven Toth <stoth@kernellabs.com>
> > ---
> >  drivers/media/dvb/frontends/cx22702.c |   23 +++++++++++++----------
> >  1 file changed, 13 insertions(+), 10 deletions(-)
> > 
> > --- linux-2.6.32-rc5.orig/drivers/media/dvb/frontends/cx22702.c	2009-10-16 09:47:14.000000000 +0200
> > +++ linux-2.6.32-rc5/drivers/media/dvb/frontends/cx22702.c	2009-10-16 09:47:45.000000000 +0200
> > @@ -92,33 +92,36 @@ static int cx22702_writereg(struct cx227
> >  
> >  	ret = i2c_transfer(state->i2c, &msg, 1);
> >  
> > -	if (ret != 1)
> > +	if (ret != 1) {
> 
> As a suggestion, if you want to optimize success paths, you should use unlikely() for error
> checks. This tells gcc to optimize the code to avoid cache cleanups for the likely condition:
> 
> 	if (unlikely(ret != 1)) {

Good point. Updated patch follows:

* * * * *

* Avoid temporary variables.
* Optimize success paths.
* Make error messages consistently verbose.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Steven Toth <stoth@kernellabs.com>
---
Changes in v2:
* Use unlikely() to help gcc optimize the success paths.

 drivers/media/dvb/frontends/cx22702.c |   23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

--- linux-2.6.35.orig/drivers/media/dvb/frontends/cx22702.c	2010-09-10 14:22:31.000000000 +0200
+++ linux-2.6.35/drivers/media/dvb/frontends/cx22702.c	2010-09-10 17:39:58.000000000 +0200
@@ -92,33 +92,36 @@ static int cx22702_writereg(struct cx227
 
 	ret = i2c_transfer(state->i2c, &msg, 1);
 
-	if (ret != 1)
+	if (unlikely(ret != 1)) {
 		printk(KERN_ERR
 			"%s: error (reg == 0x%02x, val == 0x%02x, ret == %i)\n",
 			__func__, reg, data, ret);
+		return -1;
+	}
 
-	return (ret != 1) ? -1 : 0;
+	return 0;
 }
 
 static u8 cx22702_readreg(struct cx22702_state *state, u8 reg)
 {
 	int ret;
-	u8 b0[] = { reg };
-	u8 b1[] = { 0 };
+	u8 data;
 
 	struct i2c_msg msg[] = {
 		{ .addr = state->config->demod_address, .flags = 0,
-			.buf = b0, .len = 1 },
+			.buf = &reg, .len = 1 },
 		{ .addr = state->config->demod_address, .flags = I2C_M_RD,
-			.buf = b1, .len = 1 } };
+			.buf = &data, .len = 1 } };
 
 	ret = i2c_transfer(state->i2c, msg, 2);
 
-	if (ret != 2)
-		printk(KERN_ERR "%s: readreg error (ret == %i)\n",
-			__func__, ret);
+	if (unlikely(ret != 2)) {
+		printk(KERN_ERR "%s: error (reg == 0x%02x, ret == %i)\n",
+			__func__, reg, ret);
+		return 0;
+	}
 
-	return b1[0];
+	return data;
 }
 
 static int cx22702_set_inversion(struct cx22702_state *state, int inversion)




-- 
Jean Delvare