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Date: Tue, 9 Jan 2024 11:28:54 -0800
From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: Jonathan Denose <jdenose@chromium.org>
Cc: linux-input@vger.kernel.org, Jonathan Denose <jdenose@google.com>,
	Hans de Goede <hdegoede@redhat.com>,
	Huacai Chen <chenhuacai@kernel.org>,
	Mattijs Korpershoek <mkorpershoek@baylibre.com>,
	Takashi Iwai <tiwai@suse.de>,
	Werner Sembach <wse@tuxedocomputers.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Input: i8042 - add quirk for Lenovo ThinkPad T14 Gen 1
Message-ID: <ZZ2eduF_h7lcBrSL@google.com>
References: <20230925163313.1.I55bfb5880d6755094a995d3ae44c13810ae98be4@changeid>
 <ZWF76ALANQwP_9b1@google.com>
 <CALNJtpUHHaq6g0wSuyaNBxtOE9kt6vDzdAGGu6j=JJdJmerDWQ@mail.gmail.com>
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In-Reply-To: <CALNJtpUHHaq6g0wSuyaNBxtOE9kt6vDzdAGGu6j=JJdJmerDWQ@mail.gmail.com>

Hi Jonathan,

On Mon, Nov 27, 2023 at 10:38:57AM -0600, Jonathan Denose wrote:
> Hi Dmitry
> 
> On Fri, Nov 24, 2023 at 10:45 PM Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> >
> > Hi Jonathan,
> >
> > On Mon, Sep 25, 2023 at 04:33:20PM -0500, Jonathan Denose wrote:
> > > The ThinkPad T14 Gen 1 touchpad works fine except that clicking
> > > and dragging by tapping the touchpad or depressing the touchpad
> > > do not work. Disabling PNP for controller setting discovery enables
> > > click and drag without negatively impacting other touchpad features.
> >
> > I would like to understand more on how enabling PnP discovery for i8042
> > affects the touchpad. Do you see it using different interrupt or IO
> > ports? What protocol does the touchpad use with/without PnP? If the
> > protocol is the same, do you see difference in the ranges (pressure,
> > etc) reported by the device?
> >
> > Thanks.
> >
> > --
> > Dmitry
> 
> Without PnP discovery the touchpad is using the SynPS/2 protocol, with
> PnP discovery, the touchpad is using the rmi4 protocol. Since the
> protocols are different, so are the ranges but let me know if you
> still want to see them.

Thank you for this information. So it is not PnP discovery that appears
harmful in your case, but rather that legacy PS/2 mode appears to be
working better than RMI4 for the device in question.

I will note that the original enablement of RMI4 for T14 was done by
Hans in [1]. Later T14 with AMD were added to the list of devices that
should use RMI4 [2], however this was reverted in [3].

Could you please tell me what exact device you are dealing with? What's
it ACPI ID?

[1] https://lore.kernel.org/all/20201005114919.371592-1-hdegoede@redhat.com/
[2] https://lore.kernel.org/r/20220318113949.32722-1-snafu109@gmail.com
[3] https://lore.kernel.org/r/20220920193936.8709-1-markpearson@lenovo.com

Thanks.

-- 
Dmitry