Re: [PATCH 9/13] drivers/media/tuners/fc0011.c: use macros for i2c_msg initialization

Jean Delvare
2012-10-09T12:06:55Z

On Sun, 7 Oct 2012 18:50:31 +0200 (CEST), Julia Lawall wrote:
> On Sun, 7 Oct 2012, walter harms wrote:
> > Am 07.10.2012 17:38, schrieb Julia Lawall:
> >> @@ -97,10 +96,8 @@ static int fc0011_readreg(struct fc0011_priv *priv, u8 reg, u8 *val)
> >> {
> >> u8 dummy;
> >> struct i2c_msg msg[2] = {
> >> - { .addr = priv->addr,
> >> - .flags = 0, .buf = &reg, .len = 1 },
> >> - { .addr = priv->addr,
> >> - .flags = I2C_M_RD, .buf = val ? : &dummy, .len = 1 },
> >> + I2C_MSG_WRITE(priv->addr, &reg, sizeof(reg)),
> >> + I2C_MSG_READ(priv->addr, val ? : &dummy, sizeof(dummy)),
> >> };
> >>
> >
> > This dummy looks strange, can it be that this is used uninitialised ?
>
> I'm not sure to understand the question. The read, when it happens in
> i2c_transfer will initialize dummy. On the other hand, I don't know what
> i2c_transfer does when the buffer is NULL and the size is 1. It does not
> look very elegant at least.

i2c_transfer() itself won't care, it just passes the request down to the
underlying i2c bus driver. Most driver implementations will assume
proper buffer addresses as soon as size > 0, so passing NULL instead
would crash them. In short, don't do that.

--
Jean Delvare