From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Delvare Subject: Re: I2C device driver to simutaneously support 2 devices Date: Fri, 16 May 2008 21:54:56 +0200 Message-ID: <20080516215456.097c248c@hyperion.delvare> References: <213411.97989.qm@web30304.mail.mud.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <213411.97989.qm-1S7A5l4uV2KvuULXzWHTWIglqE1Y4D90QQ4Iyu8u01E@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: i2c-bounces-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org Errors-To: i2c-bounces-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org To: Wei Liang Cc: i2c-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org List-Id: linux-i2c@vger.kernel.org Hi Wei, On Wed, 14 May 2008 23:18:46 -0700 (PDT), Wei Liang wrote: > I received this email address from Gregg Koah-Hartman. I am writing > to seek your advise on writing a I2C device driver. > > I am currently writing a device driver based on the sample code by > Gregg in Linux Journal (http://www.linuxjournal.com/article/7252). I didn't even know that Greg had been writing articles about I2C. Please note that this article is getting old, and many things it mentions have changed since then. I strongly suggest that you take a look at what i2c drivers in the current kernel tree look like, it will give you a better picture of the current situation than Greg's article. > I am new to linux device driver development and am currently attempting > to modify the code to enable it to simultaneously support 2 I2C devices > - both devices resides on different addresses. > > I have tried > adding another i2c_add_driver function in 'static int __init > tiny_init(void)' and subsequently reduplicate all functions involved in > registering a > new driver (e.g. static struct i2c_driver, i2c_detect, etc). However, > the code didn't seem to start. I have scoured through I2C > documentations in the Linux kernel and also the book Linux Device Driver > (O'Reilly) but have yet to come across any reference for the > above-mentioned task. > > I am hoping that you could provide a few pointers on how best to proceed. You definitely do not want to have more than one struct i2c_driver in your module. If you are going to support really different devices, you want to write separate modules for them. If your 2 devices are similar enough to be supported by the same driver, then a single struct i2c_driver should work fine. I don't really understand what your problem is. Having an I2C driver supporting several devices at different addresses doesn't present any special difficulty, it is the default behavior. A lot of I2C drivers in the kernel do that, just take a look at them. For example, the max6650 hardware monitoring driver supports I2C devices at 4 different addresses, and declares them with: static const unsigned short normal_i2c[] = {0x1b, 0x1f, 0x48, 0x4b, I2C_CLIENT_END}; If you write a legacy i2c driver (which is what Greg's article describes) then you would have something like the above in your module. Your i2c_driver will then attempt to attach to any I2C device living at any of the addresses in the list. -- Jean Delvare _______________________________________________ i2c mailing list i2c-GZX6beZjE8VD60Wz+7aTrA@public.gmane.org http://lists.lm-sensors.org/mailman/listinfo/i2c