From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julia Lawall Date: Tue, 09 Oct 2012 12:50:00 +0000 Subject: Re: [PATCH 2/13] drivers/media/tuners/mxl5007t.c: use macros for i2c_msg initialization Message-Id: List-Id: References: <1349624323-15584-1-git-send-email-Julia.Lawall@lip6.fr> <1349624323-15584-4-git-send-email-Julia.Lawall@lip6.fr> <20121009143035.557951bb@endymion.delvare> In-Reply-To: <20121009143035.557951bb@endymion.delvare> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jean Delvare Cc: Julia Lawall , Michael Krufky , 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 Tue, 9 Oct 2012, Jean Delvare wrote: > Hi Julia, > > On Sun, 7 Oct 2012 17:38:33 +0200, Julia Lawall wrote: > > From: Julia Lawall > > > > Introduce use of I2c_MSG_READ/WRITE/OP, for readability. > > Next time you send this patch set, please Cc me on every post so that I > don't have to hunt for them on lkml.org. OK. > > In each case, a length expressed as an explicit constant is also > > re-expressed as the size of the buffer, when this is possible. > > This is conceptually wrong, please don't do that. It is perfectly valid > to use a buffer which is larger than the message being written or read. > When exchanging multiple messages, it is actually quite common to > declare only 2 buffers and reuse them: > > char reg; > char val[2]; > > struct i2c_msg msg[2] = { > { .addr = addr, .flags = 0, .buf = ®, .len = 1 }, > { .addr = addr, .flags = I2C_M_RD, .buf = val, .len = 1 }, > }; > > reg = 0x04; > i2c_transfer(i2c_adap, msg, 2); > /* Do stuff with val */ > > reg = 0x06; > msg[1].len = 2; > i2c_transfer(i2c_adap, msg, 2); > /* Do stuff with val */ > > Your conversion would read 2 bytes from register 0x04 instead of 1 in > the example above. > > I am not opposed to the idea of i2c_msg initialization helper macros, > but please don't mix that with actual code changes which could have bad > side effects. I at least tried to check in every case that the result of sizeof is the same as the value that is present. But I can leave the constants as is, if that seems better. Thanks for the feedback. julia