linux-kernel - Re: [BUG] Stuck key syndrome (was: Re: [PATCH net-next v2] net: dsa: microchip: Add SGMII port support to KSZ9477 switch)

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Message-ID: <im4cvmgjmdztjsvhorxt77t43o4a7rixoqyawp67jwijsg4vpn@jdl7m75ts2pc>
Date: Wed, 7 May 2025 10:23:37 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Maxime Chevallier <maxime.chevallier@...tlin.com>, 
	"Russell King (Oracle)" <linux@...linux.org.uk>, Andrew Lunn <andrew@...n.ch>, 
	Woojung Huh <woojung.huh@...rochip.com>, Vladimir Oltean <olteanv@...il.com>, 
	Heiner Kallweit <hkallweit1@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG] Stuck key syndrome (was: Re: [PATCH net-next v2] net: dsa:
 microchip: Add SGMII port support to KSZ9477 switch)

On Wed, May 07, 2025 at 07:46:03AM -0700, Linus Torvalds wrote:
> On Wed, 7 May 2025 at 04:51, Maxime Chevallier
> <maxime.chevallier@...tlin.com> wrote:
> >
> > So, same as you, it'll take a long time for me to say with some amount
> > of certainty that 'i8042_unlock=1' has a beneficial effect, of
> > course unless I see the problem happen again in the meantime.
> 
> Christ. You'd expect that any i8042 issues had been fixed long ago,
> but the problem is that the chip doesn't necessarily even exist in
> modern platforms, and everybody just fakes it.

It has not existed as a real chip for more than 20 years I believe. It's
all faked in firmware and embedded controllers that fake it in their
firmwares.

And newer firmware tend to implement less and less of it, just what OS
that devices that ship with it needs.

> 
> So the platform presumably still has hardware support for it, but it's
> mostly in the form of "take a trap when accessing the legacy keyboard
> ports, and fake it in firmware".
> 
> Although it doesn't help that there are literally decades of clone
> chips and hacky real hardware that extended on the i8042 in various
> more-or-less compatible ways.
> 
> Which makes all of these things almost entirely undebuggable.
> 
> I'm surprised the XPS9510 would be particularly troublesome - I've had
> an XPS for years (older version, obviously) with no issues outside of
> WiFi sometimes acting up. But random firmware...
> 
> I doubt it's "keylock active", but who knows. I get that on my xps
> too, it's a random bit that doesn't really mean much. But - because of
> all the reasons above - who knows...

It is typically harmless and whats more trying to "unlock" 8042 when it
reports being locked might confuse 8042 emulation.

Thanks.

-- 
Dmitry