Re: [PATCH 2/2] input: egalax_ts: free irq resource before request the line as GPIO

[Linus Walleij <linus.walleij@linaro.org>]

On Sun, Apr 19, 2020 at 8:10 PM Dmitry Torokhov
<dmitry.torokhov@gmail.com> wrote:
> On Tue, Mar 10, 2020 at 07:15:35AM +0000, BOUGH CHEN wrote:
> >
> > > From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> > > Sent: 2020年3月10日 12:27
> > > To: BOUGH CHEN <haibo.chen@nxp.com>
> > > Cc: linux-input@vger.kernel.org; dl-linux-imx <linux-imx@nxp.com>
> > > Subject: Re: [PATCH 2/2] input: egalax_ts: free irq resource before request
> > > the line as GPIO
> > >
> > > On Tue, Feb 11, 2020 at 04:41:12PM +0800, haibo.chen@nxp.com wrote:
> > > > From: Haibo Chen <haibo.chen@nxp.com>
> > > >
> > > > + egalax_free_irq(ts);
> > >
> > > It sounds to me you want simply disable interrupts in suspend. Does not
> > > calling disable_irq() here suffice?
> >
>
> > Here why I want to disable interrupts here is because in the newest
> > gpio system, if the gpio is request as an irq, it can't be request as
> > a gpio anymore.  In the function egalax_wake_up_device(), we need to
> > request the irq pin as a gpio for a while, generate a signal to wake
> > up the device. So before request the pad as gpio, need first free irq
> > resource.
>
> This seems like a fairly common pattern and I wonder if our GPIO
> overlords can help us here.
>
> Linus, Mika, Andy, would it be possible to have an API that would allow
> driver to temporarily "take over" GPIO that is used for interrupts and
> drive it as output without resorting to freeing and re-acquiring irq?
> I.e. something like gpiod_irq_drive_output_start() and
> gpiod_irq_drive_output_end()?

Hans Verkuil had exactly this problem in the CEC GPIO driver,
drivers/media/platform/cec-gpio/cec-gpio.c

If you call disable_irq() on an irqchip implemented in a GPIO
driver using the generic GPIOLIB_IRQCHIP helper library (which
I really recommend) then the line can be switched to output,
used like such, then switched to input and enable_irq() be
called again.

See these commits:
commit 4e9439ddacea06f35acce4d374bf6bd0acf99bc8
"gpiolib: add flag to indicate if the irq is disabled"
commit 461c1a7d4733d1dfd5c47b040cf32a5e7eefbc6c
"gpiolib: override irq_enable/disable"

If your corresponding GPIO driver does not use GPIOLIB_IRQCHIP
then you have a bigger problem and we need to look into that.

Yours,
Linus Walleij