Implementing a new driver

Implementing a new driver

[Alessio Sangalli]

Hi, I would like to implement a driver for an I2C interface we are
implementing in a chip.

This interface will be used to read DDC/EDID data from monitors.

I have never worked with the I2C subsystem (only lm-sensors as a user,
without deepening my knowledge on the actual drivers).

Can you give me a checklist of things to do for this task so that I can
get started for implementation?

Thanks
Alessio

Re: Implementing a new driver

[Jean Delvare]

Hi Alessio,

On Fri, 23 Jan 2009 01:28:13 -0800, Alessio Sangalli wrote:
> Hi, I would like to implement a driver for an I2C interface we are
> implementing in a chip.
> 
> This interface will be used to read DDC/EDID data from monitors.
> 
> I have never worked with the I2C subsystem (only lm-sensors as a user,
> without deepening my knowledge on the actual drivers).
> 
> Can you give me a checklist of things to do for this task so that I can
> get started for implementation?

As a quick starting point I recommend this FAQ item:
http://i2c.wiki.kernel.org/index.php/Linux_2.6_I2C_development_FAQ#New_I2C_bus_drivers

If you have more detailed questions while writing the code, post them
on the list and we'll try to help.

-- 
Jean Delvare

Re: Implementing a new driver

[Alessio Sangalli]

Jean Delvare wrote:

> As a quick starting point I recommend this FAQ item:
> http://i2c.wiki.kernel.org/index.php/Linux_2.6_I2C_development_FAQ#New_I2C_bus_drivers


Thanks, this will be useful to get started; anyway, it implies a
knowledge of what is a "bus driver" or a "chip driver". I've read other
articles but I'm still a bit confused. Could you give me a very very
quick description of all kind of i2c-related drivers?

What is the preferred way to actually test the driver, I am quite
comfortable with a solder iron if I have to connect a simple device to
try a connection

bye!
as

Re: Implementing a new driver

[Jean Delvare]

Hi Alessio,

On Fri, 23 Jan 2009 09:31:30 -0800, Alessio Sangalli wrote:
> Jean Delvare wrote:
> 
> > As a quick starting point I recommend this FAQ item:
> > http://i2c.wiki.kernel.org/index.php/Linux_2.6_I2C_development_FAQ#New_I2C_bus_drivers
> 
> Thanks, this will be useful to get started; anyway, it implies a
> knowledge of what is a "bus driver" or a "chip driver". I've read other
> articles but I'm still a bit confused. Could you give me a very very
> quick description of all kind of i2c-related drivers?

Basically, the bus drivers give you access to the I2C bus, while the
chip drivers are specific to devices which are connected to the bus.
This is essentially similar to USB, where you need a driver for the
host controller, and then a driver for devices connected to the USB
ports.

You may want to read this page on the wiki:
http://i2c.wiki.kernel.org/index.php/Driver_Architecture
and the document linked at the bottom of the page.

Examples of I2C bus drivers can be found under drivers/i2c/busses.
Examples of I2C chip drivers can be found under drivers/rtc (for RTC
chips), drivers/hwmon (for hardware monitoring chips) or drivers/gpio
(for I/O expanders.)

> What is the preferred way to actually test the driver, I am quite
> comfortable with a solder iron if I have to connect a simple device to
> try a connection

If you have an AT24C02 EEPROM at hand or similar, you'll be able to
test most of the transaction types. But actually, any I2C or SMBus chip
you can connect to the bus should be good enough to test the basics of
your i2c bus driver.

-- 
Jean Delvare

Re: Implementing a new driver

[Alessio Sangalli]

Jean Delvare wrote:

> Examples of I2C chip drivers can be found under drivers/rtc (for RTC


Thanks. I guess there is already a driver for DDC/EDID monitor
parameters right? Should be a fairly common feature for graphic cards

bye!
as

Re: Implementing a new driver

[Jean Delvare]

Hi Alessio,

On Fri, 23 Jan 2009 13:35:28 -0800, Alessio Sangalli wrote:
> Jean Delvare wrote:
> 
> > Examples of I2C chip drivers can be found under drivers/rtc (for RTC
> 
> 
> Thanks. I guess there is already a driver for DDC/EDID monitor
> parameters right? Should be a fairly common feature for graphic cards

See drivers/video/fb_ddc.c and drivers/video/edid.h, presumably this is
what you want for a framebuffer driver. For an X driver, the code
handling DDC is in X itself.

Or, for testing purpose, you can use the legacy "eeprom" driver
together with the ddcmon and decode-edid scripts from i2c-tools [1].

[1] http://www.lm-sensors.org/wiki/I2CTools

-- 
Jean Delvare