linux-kernel - Re: kernel panic with simple driver

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Date:	Wed, 10 Aug 2011 12:35:24 +1000
From:	Ryan Mallon <rmallon@...il.com>
To:	"Murali K. Vemuri" <vemuri.muralikrishna@...il.com>
CC:	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org
Subject: Re: kernel panic with simple driver

On 10/08/11 12:29, Murali K. Vemuri wrote:
> On Wed, Aug 10, 2011 at 11:16 AM, Greg KH<greg@...ah.com>  wrote:
>> On Wed, Aug 10, 2011 at 10:33:28AM +0900, Murali K. Vemuri wrote:
>>> There is no concurrent access to the timer. The design is that:
>>> 1.Driver provides an IOCTL for start / stop
>>> 2. when the driver receives START IOCTL, it toggles some GPIOs to ON / OFF.
>>> 3. the GPIOs will be ON for 500 MSec and OFF for 500 MSec.
>>> 4. Two successive START IOCTLs will not be honored.
>>> 5. There is only one application that uses these IOCTLs
>>> 6. When I receive a STOP IOCTL, I am doing :
>>> if (timer_pending (&my_timer))
>>> del_timer(&my_timer);
>> What kind of driver is this?  For what type of hardware?
>>
>> Can't you control the gpios from userspace with out any need to write a
>> kernel driver?
>>
> This driver is meant for controlling some LEDs. The CPU is OMAP 3530
> and the OS is Android.
>  From the user space, I could not control the GPIOs directly, and thus
> I ended up supporting in the form of a simple driver.
> I agree that these are better done from the user space, but as much as
> I google'd studied, I could not find any better way to implement this.
>
> If anyone has more info, that is also highly appreciated.

If you have CONFIG_GPIO_SYSFS enabled then you can access the gpios 
directly via sysfs. See Documentation/gpio.txt for details.

~Ryan

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