How to choeck for a gpio-keys based switch state?

How to choeck for a gpio-keys based switch state?

[Janusz Krzysztofik]

Hi,

Greetings from new list member.

I am trying to create a gpio-keys based platform device driver for a 
hook switch. I am wondering if there is a possibility to check for the 
switch state before the first event comes up. I think this feature could 
be essential for correct user experience - an application should know 
the switch state from the start.
As I am not able to find such functionality in the current gpio-keys 
driver, I wonder if this could be done over gpiolib sysfs interface by 
adding optional gpio_export() call to the driver init function. I can 
try to provide a patch if this sounds reasonable to you.

Thanks,
Janusz

Re: How to choeck for a gpio-keys based switch state?

[Dmitry Torokhov]

Hi Janusz,

On Fri, May 15, 2009 at 05:47:55PM +0200, Janusz Krzysztofik wrote:
> Hi,
>
> Greetings from new list member.
>
> I am trying to create a gpio-keys based platform device driver for a  
> hook switch. I am wondering if there is a possibility to check for the  
> switch state before the first event comes up. I think this feature could  
> be essential for correct user experience - an application should know  
> the switch state from the start.
> As I am not able to find such functionality in the current gpio-keys  
> driver, I wonder if this could be done over gpiolib sysfs interface by  
> adding optional gpio_export() call to the driver init function. I can  
> try to provide a patch if this sounds reasonable to you.
>

Your application should use EVIOCGSW ioctl to query the initial state of
the switches.

-- 
Dmitry

Re: How to choeck for a gpio-keys based switch state?

[Janusz Krzysztofik]

Hi Dimitry,

Thanks for you answer.

Friday 15 May 2009 20:58:06 you wrote:
> Your application should use EVIOCGSW ioctl to query the initial state of
> the switches.

I see. Is this ioctl query the only way of getting a switch state from 
userspace? Do you know of a utility that could be used from a shell script to 
check for the state?
Or maybe you could suggest a different approach, better than using gpio-keys 
for the purpose of driving a phone hook switch? Maybe something like rfkill 
device, that exposes its state over sysfs in addition to providing input 
events, would be better for this purpose?

Thanks,
Janusz