linux-kernel - Re: Emulating level IRQs

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Date:	Sun, 05 Aug 2012 18:22:51 +0200
From:	Daniel Mack <zonque@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Sven Neumann <s.neumann@...mfeld.com>,
	Olof Johansson <olof@...om.net>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Eric Miao <eric.y.miao@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Emulating level IRQs

On 24.07.2012 20:01, Daniel Mack wrote:
> On 23.07.2012 18:51, Dmitry Torokhov wrote:
>> On Thu, Jul 19, 2012 at 05:36:12PM +0200, Daniel Mack wrote:
> 
>>> Ok, finally I found some time. In general, the patch works fine. The
>>> only detail I had to amend was the irqflags, which were changed from
>>> IRQF_TRIGGER_RISING/IRQF_TRIGGER_FALLING to
>>> IRQF_TRIGGER_HIGH/IRQF_TRIGGER_LOW, which doesn't work as the PXA can't
>>> deal with level-based IRQs. Changing this back to RISING/FALLING makes
>>> the driver work again.
>>
>> Hmm, but that would mean we need to restore reading the data in open()
>> to make sure we re-arm IRQ in case somebody touched the screen before it
>> was opened by userspace...
> 
> I had another look at this and don't really know what to do here. We
> definitely need level interrupts for this device as the interrupt line's
> level is the only that tells us when we can stop reading from the
> device. So it's not just the start condition that bites us here.
> 
> I copied some people that might help find a solution.
> 
> To summarize the problem: The EETI touchscreen is a device that asserts
> a GPIO line when it has events to deliver and waits for I2C commands to
> empty its buffers. When there are no more buffered events, it will
> de-assert the line.
> 
> This device is connected to a PXA GPIO that is only able to deliver edge
> IRQs, and the old implemenation was to wait for an interrupt and then
> read data as long as the IRQ's corresponding GPIO was asserted. However,
> expecting that an IRQ is mappable to a GPIO is not something we should
> do, so the only clean solution is to teach the PXA GPIO controller level
> IRQs.
> 
> So it boils down to the question: Is there any easy and generic way to
> emulate level irq on chips that don't support that natively?

Otherwise, we would need some sort of generic irq_to_gpio() again, and
the interrupt line the driver listens to must have support for that sort
of mapping.

Any opinion on this, anyone?



Thanks,
Daniel

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