linux-kernel - Re: [PATCH 9/13] drivers/media/tuners/fc0011.c: use macros for i2c

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Date:	Sun, 7 Oct 2012 20:05:01 +0200
From:	Michael Büsch <m@...s.ch>
To:	Julia Lawall <julia.lawall@...6.fr>
Cc:	walter harms <wharms@....de>, kernel-janitors@...r.kernel.org,
	rmallon@...il.com, shubhrajyoti@...com,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/13] drivers/media/tuners/fc0011.c: use macros for
 i2c_msg initialization

On Sun, 7 Oct 2012 18:50:31 +0200 (CEST)
Julia Lawall <julia.lawall@...6.fr> wrote:

> >> @@ -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.

Well its use case is if you only care about the side effects and not the actual data
returned by the read operation.

-- 
Greetings, Michael.

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