linux-kernel - Re: [PATCH 2/2] Input: ili210x

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Date:   Mon, 4 Nov 2019 17:25:23 -0600
From:   Adam Ford <aford173@...il.com>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     Marek Vasut <marex@...x.de>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] Input: ili210x - add ILI2117 support

On Mon, Nov 4, 2019 at 3:43 PM Sven Van Asbroeck <thesven73@...il.com> wrote:
>
> Hi Adam,
>
> On Mon, Nov 4, 2019 at 4:28 PM Adam Ford <aford173@...il.com> wrote:
> >
> > I am using IRQ_TYPE_EDGE_RISING for the 2117A.  Is that correct?  For
> > my touchscreen, the IRQ line is low until a touch is detected, so I
> > assume we want to capure on the rising edge.
>
> That is correct for the 2117A, as far as I know. I am using the same
> setting.
>
> >
> > Regarding Dmitry's patch,
> > Is it a good idea to use msleep in an IRQ?  It seems like using the
> > schedule_delayed_work() call seems like it will get in and get out of
> > the ISR faster.
> >
> > If we use msleep and scan again, isn't it possible to starve other processes?
>
> I believe using msleep() is ok because this is not a "real" interrupt handler,
> but a threaded one. It runs in a regular kernel thread, with its interrupt
> turned off (but all other interrupts remain enabled). Its interrupt is
> re-enabled automatically after the threaded handler returns.
>
> See
> https://elixir.bootlin.com/linux/latest/source/include/linux/interrupt.h#L50
>
> > > @@ -268,7 +278,7 @@ static irqreturn_t ili210x_irq(int irq, void *irq_data)
> > >                 }
> > >
> > >                 touch = ili210x_report_events(priv, touchdata);
> > > -               keep_polling = touch || chip->continue_polling(touchdata);
> > > +               keep_polling = chip->continue_polling(touchdata, touch);
> > >                 if (keep_polling)
> >
> > Why not just check the value of touch instead of invoking the function
> > pointer which takes the value of touch in as a parameter?
> >
>
> The value of touch must be checked inside the callback, because
> some variants use it to decide if they should poll again, and
> some do not, such as the ili211x.

That makes sense.
>
> If I have misinterpreted your suggestion, could you perhaps
> express it in C, so I can understand better?

You explained it.
I'm good.

adam