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

Mauro Carvalho Chehab
2010-09-10T15:13:22Z

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)) {

> 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 (ret != 2) {

Same comment applies here.

> + 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)
>