On Fri, 2012-07-20 at 16:24 +0530, aurum spark wrote:

Hi All,

I have written and seen lot of code of i2c drivers for input subsystem devices and much familiar with that. Now I have started writing driver for one chip that is not exactly type of input device. So, little bit confused about how should be the driver architecture so that it will be a clean code yet simple. Following text and diagram explains short functional description of chip.

Chip Interface :- ==========

====== ======= | | | I2C | | | ----- I2C --- | Device | | ARM | ----- Bus -- | With rw | ------------ Input Connect | | | regs | | | ---------------| | ====== INTR =======

So above picture depicts how chip is interfaced to ARM CPU. This chip has some registers which are rw and can be used to read certain information from chip or to program it. This chip is capable of giving intterupt to CPU. This chip has one input which it like some cable connection. It detects when this cable is connected and raises the interrupt.

Functionality Expected in Driver:- ===================

1. Driver should communicate with chip over I2C. 2. Driver should report event to user space upon receiving interrupt from I2C device. 3. Driver should be capable of programming I2C chip @ the time of initialization as well should be capable of changing registers as and when Linux User Space application wants to.

What I have thought of:- ==============

#1 definitely makes this as i2c client driver(chip driver)

#2 Here I have few options

a) Shall I use input subsystem mechanism to report interrupt as an event to user space ? In this case it's combination of I2C + input subsystem. Then application can read something over i2c and decide next flow,

OR

b) Shall I use some sysfs based interface on which application can do select sys call and can receive event ? for this nothing extra required.

#3 Since approach in #2 is not fixed here also there are multiple options a) This can be written as I2C client + char driver so that it can have ioctls to send commands to i2c chip based on applications demand. What does this chip do and why does it need to do I2C transaction based on application demand? b) We can provide sysfs interface to user space to send commands to i2c device as and when required at runtime.

As per my thoughts I am not sure shall I make this as input device just to report one event upon getting interrupt from device. Also will it be ok to have this as char driver in combination with i2c chip driver ? Please guide me and take me to correct source or documentation or to source code of some driver for this kind of device. Does i2c support ops like fbops ?

Regards, ~/Aurum

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