lkml.org 
[lkml]   [2020]   [May]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] gpiolib: add GPIO_SET_DEBOUNCE_IOCTL
On Mon, May 25, 2020 at 02:17:41PM +0200, Linus Walleij wrote:
> On Mon, May 25, 2020 at 4:22 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> > You mention timers for the gpio pins that cannot provide debounce,
> > so I'm confused. Could you clarify which strategy you have in mind?
>
> My idea is that the callback gpiod_set_debounce() for in-kernel consumers
> should more or less always return success. Either the hardware does
> the debounce, or gpiolib sets up a timer.
>
> > I've also had a quick look at the possibility of providing the software
> > debounce for in-kernel consumers.
>
> That is where I think it should start.
>
> > Are you anticipating new API for
> > that? e.g. allowing consumers to request gpio events? Cos, gpio_keys
> > grabs the irq itself - and that would bypass the software debouncer,
> > or even conflict with it.
>
> It may be hard or impossible.
>
> I suppose gpiolib would have to steal or intercept the interrupt
> by using e.g. IRQF_SHARED and then just return IRQ_HANDLED
> on the first IRQ so the underlying irq handler does not get called.
>

And how would gpiolib ensure that it was first in the chain?

> After the timer times out it needs to retrigger the IRQ.
>
> So the consuming driver would se a "debounced and ready"
> IRQ so when it gets this IRQ it knows for sure there is
> no bounciness on it because gpiolib already took care
> of that.
>
> The above is in no way trivial, but it follows the design pattern
> of "narrow and deep" APIs.
>

Totally agree with the concept - just trying to work out how to
implement it seemlessly given the existing API and usage, and given my
limited knowledge of the kernel internals.

> Failure is an option! Sorry if I push too complex ideas.
>

I'm not as concerned about complexity as I am about fragility.

I don't see any problem adding debounce for gpiolib-cdev.
Adding a more complete solution to gpiolib itself is certainly
non-trivial, if it is possible at all.

The path I'll probably be taking is adding a debouncer to gpiolib-cdev,
so at least we have a solution for userspace, then take a longer look at
the more general solution.

Cheers,
Kent.

\
 
 \ /
  Last update: 2020-05-25 17:18    [W:0.085 / U:5.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site