linux-kernel - Re: [PATCH v4 7/7] Input: Add "inhibited" property

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Date:   Tue, 6 Oct 2020 18:11:02 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Andrzej Pietrasiewicz <andrzej.p@...labora.com>
Cc:     linux-pm@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-input@...r.kernel.org,
        linux-tegra@...r.kernel.org, patches@...nsource.cirrus.com,
        ibm-acpi-devel@...ts.sourceforge.net,
        platform-driver-x86@...r.kernel.org,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Sylvain Lemieux <slemieux.tyco@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Barry Song <baohua@...nel.org>,
        Michael Hennerich <michael.hennerich@...log.com>,
        Nick Dyer <nick@...anahar.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Ferruh Yigit <fery@...ress.com>,
        Sangwon Jee <jeesw@...fas.com>,
        Peter Hutterer <peter.hutterer@...hat.com>,
        Henrique de Moraes Holschuh <ibm-acpi@....eng.br>,
        kernel@...labora.com, Patrik Fimml <patrikf@...omium.org>
Subject: Re: [PATCH v4 7/7] Input: Add "inhibited" property

On Tue, Oct 06, 2020 at 03:04:28PM +0200, Andrzej Pietrasiewicz wrote:
> Hi Dmitry,
> 
> W dniu 05.10.2020 o 20:10, Dmitry Torokhov pisze:
> > Hi Andrzej,
> > 
> > On Mon, Jun 08, 2020 at 01:22:11PM +0200, Andrzej Pietrasiewicz wrote:
> > > @@ -284,8 +284,11 @@ static int input_get_disposition(struct input_dev *dev,
> > >   	case EV_KEY:
> > >   		if (is_event_supported(code, dev->keybit, KEY_MAX)) {
> > > -			/* auto-repeat bypasses state updates */
> > > -			if (value == 2) {
> > > +			/*
> > > +			 * auto-repeat bypasses state updates but repeat
> > > +			 * events are ignored if the key is not pressed
> > > +			 */
> > > +			if (value == 2 && test_bit(code, dev->key)) {
> > >   				disposition = INPUT_PASS_TO_HANDLERS;
> > >   				break;
> > >   			}
> > 
> > Is this chunk really part of inhibit support? I'd think we cancel
> > autorepeat timer when we are releasing a key, no?
> > 
> 
> When I look at it now it seems to me the chunk might be redundant.
> But let me explain what I had in mind when adding it.
> 
> It is a matter of what we do with input events generated while a
> device is inhibited. If ->open()/->close() are not provided by the
> driver then inhibiting amounts to merely ignoring input events from
> a device while it remains active. What else can you do if the driver
> does not provide a method to prepare the device for generating events/
> to stop generating events?
> 
> In this special case a user might trigger a repeated event while the
> device is inhibited, then the user keeps holding the key down and the
> device is uninhibited. Do we pass anything to handlers then?
> 
> In my opinion we should not. Such an event is "illegal" in a sense that it
> was generated at a time when nobody wanted any events from the device.
> Hence the test to let only those auto-repeat events through for which
> a key is actually pressed.
> 
> However, what I see now is that if a device is inhibited, no key
> will ever reach neither the "1" nor "2" state because of the "if"
> in the very beginning of input_handle_event().

OK, then let's drop it for now. We can revisit if we see that a problem.

Thanks.

-- 
Dmitry