linux-kernel - Re: [PATCH v5] Fix freeze in lm8333 i2c keyboard driver

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Date:   Fri, 12 May 2023 18:55:08 +0200
From:   Tomáš Mudruňka <tomas.mudrunka@...il.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Jeff LaBundy <jeff@...undy.com>, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] Fix freeze in lm8333 i2c keyboard driver

> So this is still racy, isn't it? The interrupt may come after read is
> done, but before we register the handler.

Well. It is. But please see the rest of the thread, where we've
already discussed this.

Every time the interrupt handler runs, the interrupt is disabled and
then reenabled after i2c communication is done. Which means this exact
thing happens on each keypress anyway. So i don't think it's a
necessarily huge deal. It might not be perfect solution, but it makes
things much better. window in which the deadlock condition can happen
is now in range of few ms (or us), instead of ~10 seconds (previously
it included bootloader and basicaly any moment from power up to driver
load)

Another solution would be to trigger on LOW instead of FALLING as
proposed in initial version of the patch. That would be safer in terms
of lm8333 deadlock, but Jeff was concerned about possibility of
interrupt storm taking down whole system in case the IRQ line gets
stuck in LOW for some reason...

Tom

pá 12. 5. 2023 v 1:44 odesílatel Dmitry Torokhov
<dmitry.torokhov@...il.com> napsal:
>
> On Wed, May 03, 2023 at 08:44:06PM -0500, Jeff LaBundy wrote:
> > Hi Tomas,
> >
> > On Wed, May 03, 2023 at 05:32:31PM +0200, Tomas Mudrunka wrote:
> > > LM8333 uses gpio interrupt line which is triggered by falling edge.
> > > When button is pressed before driver is loaded,
> > > driver will miss the edge and never respond again.
> > > To fix this we run the interrupt handler before registering IRQ
> > > to clear the interrupt via i2c command.
> > >
> > > Signed-off-by: Tomas Mudrunka <tomas.mudrunka@...il.com>
> > > ---
> >
> > Reviewed-by: Jeff LaBundy <jeff@...undy.com>
> >
> > >  drivers/input/keyboard/lm8333.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/input/keyboard/lm8333.c b/drivers/input/keyboard/lm8333.c
> > > index 7457c3220..52108c370 100644
> > > --- a/drivers/input/keyboard/lm8333.c
> > > +++ b/drivers/input/keyboard/lm8333.c
> > > @@ -178,6 +178,8 @@ static int lm8333_probe(struct i2c_client *client)
> > >                     dev_warn(&client->dev, "Unable to set active time\n");
> > >     }
> > >
> > > +   lm8333_irq_thread(client->irq, lm8333);
>
> So this is still racy, isn't it? The interrupt may come after read is
> done, but before we register the handler.
>
> > > +
> > >     err = request_threaded_irq(client->irq, NULL, lm8333_irq_thread,
> > >                                IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
> > >                                "lm8333", lm8333);
> > > --
> > > 2.40.1
> >
>
> Thanks.
>
> --
> Dmitry