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

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Date:   Mon, 4 Nov 2019 15:36:21 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Adam Ford <aford173@...il.com>
Cc:     Sven Van Asbroeck <thesven73@...il.com>,
        Marek Vasut <marex@...x.de>, 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 04, 2019 at 05:25:23PM -0600, Adam Ford wrote:
> 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.

OK, I refreshed the branch with fixes and a couple of new patches. It is
on top of 5.3 now. If this works for you guys I will be merging it for
5.5.

Thanks.

-- 
Dmitry