I2C device driver to simutaneously support 2 devices

Hi,

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 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. Thanks in advance.

Cheers,
Wei Liang

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Hi Wei,

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.

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

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