Need help: Watchdog-driver over smbus (i2c)

Need help: Watchdog-driver over smbus (i2c)

[Sven Anders]

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Hello!

I'm trying to code a watchdog driver for the Winbond w83793g chip. I
already coded a watchdog for another Winbond chip before, but for
this I need to access it over the system managment bus (or more
specific the i2c, client address 2E).

I already coded the detection and initialization routines, but now I
need some help, because I do not know how to use the i2c framework
together with the watchdog framework.
All other drivers I found are using the sysfs framework. This functions
use the to_i2c_client() function to get a pointer to the i2c client.

I tried to store the i2c client pointer to a global variable, to use
it later in the watchdog functions.
But when I try to use the "i2c_smbus_read_byte_data()" or
"i2c_smbus_write_byte_data()" functions, I will get a kernel OOPS
(without any hw-sensors driver loaded!).

What is the best method to get the watchdog framework (i.e. the open,
close, write, read and ioctl functions) to work with the i2c framework?


Moreover the w83793g hardware sensors driver may already
accessing the same chip. What is the normal way to deal with this?


Regards
 Sven Anders

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Re: Need help: Watchdog-driver over smbus (i2c)

[Jean Delvare]

Hallo Sven,

On Mon, 30 Nov 2009 22:30:07 +0100, Sven Anders wrote:
> I'm trying to code a watchdog driver for the Winbond w83793g chip. I
> already coded a watchdog for another Winbond chip before, but for
> this I need to access it over the system managment bus (or more
> specific the i2c, client address 2E).
> 
> I already coded the detection and initialization routines, but now I
> need some help, because I do not know how to use the i2c framework
> together with the watchdog framework.
> All other drivers I found are using the sysfs framework. This functions
> use the to_i2c_client() function to get a pointer to the i2c client.
> 
> I tried to store the i2c client pointer to a global variable, to use
> it later in the watchdog functions.
>
> But when I try to use the "i2c_smbus_read_byte_data()" or
> "i2c_smbus_write_byte_data()" functions, I will get a kernel OOPS
> (without any hw-sensors driver loaded!).
> 
> What is the best method to get the watchdog framework (i.e. the open,
> close, write, read and ioctl functions) to work with the i2c framework?

The fact that the device is accessed over I2C/SMBus doesn't change
anything to the watchdog interface. It is only an implementation detail
for the way the data registers are accessed.

> Moreover the w83793g hardware sensors driver may already
> accessing the same chip. What is the normal way to deal with this?

Do not write a separate driver for the watchdog functionality. Instead,
add the functionality to the existing hwmon/w83793.c driver. Otherwise
both features will be mutually exclusive.

An example of how this can be done is in hwmon/fschmd.c [1] if you want
to take a look. This is an I2C/SMBus device driver as well, so your code
should be very similar in the end.

[1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=drivers/hwmon/fschmd.c

Hope this helps,
-- 
Jean Delvare

Re: Need help: Watchdog-driver over smbus (i2c)

[Sven Anders]

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Jean Delvare schrieb:
> Hallo Sven,
> 
> On Mon, 30 Nov 2009 22:30:07 +0100, Sven Anders wrote:
>
>> Moreover the w83793g hardware sensors driver may already
>> accessing the same chip. What is the normal way to deal with this?
> 
> Do not write a separate driver for the watchdog functionality. Instead,
> add the functionality to the existing hwmon/w83793.c driver. Otherwise
> both features will be mutually exclusive.
> 
> An example of how this can be done is in hwmon/fschmd.c [1] if you want
> to take a look. This is an I2C/SMBus device driver as well, so your code
> should be very similar in the end.
> 
> [1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=drivers/hwmon/fschmd.c
> 
> Hope this helps,

Yes, thanks! This was the hint I needed.
Now I finished the watchdog driver and it's working!

Regards
 Sven Anders

-- 
 Sven Anders <anders-3bOZC6EutKuELgA04lAiVw@public.gmane.org>                 () Ascii Ribbon Campaign
                                                 /\ Support plain text e-mail
 ANDURAS service solutions AG
 Innstrasse 71 - 94036 Passau - Germany
 Web: www.anduras.de - Tel: +49 (0)851-4 90 50-0 - Fax: +49 (0)851-4 90 50-55

Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety.
  - Benjamin Franklin

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Re: Need help: Watchdog-driver over smbus (i2c)

[Jean Delvare]

On Thu, 03 Dec 2009 21:56:59 +0100, Sven Anders wrote:
> Jean Delvare schrieb:
> > Hallo Sven,
> > 
> > On Mon, 30 Nov 2009 22:30:07 +0100, Sven Anders wrote:
> >
> >> Moreover the w83793g hardware sensors driver may already
> >> accessing the same chip. What is the normal way to deal with this?
> > 
> > Do not write a separate driver for the watchdog functionality. Instead,
> > add the functionality to the existing hwmon/w83793.c driver. Otherwise
> > both features will be mutually exclusive.
> > 
> > An example of how this can be done is in hwmon/fschmd.c [1] if you want
> > to take a look. This is an I2C/SMBus device driver as well, so your code
> > should be very similar in the end.
> > 
> > [1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=drivers/hwmon/fschmd.c
> > 
> > Hope this helps,
> 
> Yes, thanks! This was the hint I needed.
> Now I finished the watchdog driver and it's working!

Cool. When it's ready, please send it over to the lm-sensors list so
that it gets merged.

-- 
Jean Delvare