From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Delvare Date: Tue, 09 Oct 2012 12:06:17 +0000 Subject: Re: [PATCH 9/13] drivers/media/tuners/fc0011.c: use macros for i2c_msg initialization Message-Id: <20121009140617.6b2a159a@endymion.delvare> List-Id: References: <1349624323-15584-1-git-send-email-Julia.Lawall@lip6.fr> <1349624323-15584-11-git-send-email-Julia.Lawall@lip6.fr> <5071B147.3010708@bfs.de> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Julia Lawall Cc: walter harms , Michael Buesch , kernel-janitors@vger.kernel.org, rmallon@gmail.com, shubhrajyoti@ti.com, Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org 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 = ®, .len = 1 }, > >> - { .addr = priv->addr, > >> - .flags = I2C_M_RD, .buf = val ? : &dummy, .len = 1 }, > >> + I2C_MSG_WRITE(priv->addr, ®, 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