linux-kernel - Re: [PATCH 2/2] arm64: dts: qcom: sc8280xp-x13s: Fix/enable touchscreen

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Message-ID: <20240126130232.GA5506@aspen.lan>
Date: Fri, 26 Jan 2024 13:02:32 +0000
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Bjorn Andersson <quic_bjorande@...cinc.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Johan Hovold <johan+linaro@...nel.org>,
	linux-arm-msm@...r.kernel.org, linux-input@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Konrad Dybcio <konrad.dybcio@...ainline.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH 2/2] arm64: dts: qcom: sc8280xp-x13s: Fix/enable
 touchscreen

On Fri, Jan 26, 2024 at 09:12:37AM +0100, Johan Hovold wrote:
> On Thu, Jan 25, 2024 at 07:55:14PM -0800, Bjorn Andersson wrote:
> > The failing read-test in __i2c_hid_core_probe() determines that there's
> > nothing connected at the documented address of the touchscreen.
> >
> > Introduce the 5ms after-power and 200ms after-reset delays found in the
> > ACPI tables. Also wire up the reset-gpio, for good measure.
>
> As the supplies for the touchscreen are always on (and left on by the
> bootloader) it would seem that it is really the addition of the reset
> gpio which makes things work here. Unless the delay is needed for some
> other reason.
>
> (The power-on delay also looks a bit short compared to what is used for
> other devices.)
>
> Reset support was only recently added with commit 2be404486c05 ("HID:
> i2c-hid-of: Add reset GPIO support to i2c-hid-of") so we should not
> backport this one before first determining that.

This comment attracted my attention so I tried booting with each of the
three lines individually.


On Thu, Jan 25, 2024 at 07:55:14PM -0800, Bjorn Andersson wrote:
> +             reset-gpios = <&tlmm 99 GPIO_ACTIVE_LOW>;

This is not enough, on it's own, to get the touch screen running.

I guess that's not so much of a surprise since the rebind-the-driver
from userspace trick wouldn't have been touching this reset.


> +             post-power-on-delay-ms = <5>;

This line alone is enough (in v6.7.1).


> +             post-reset-deassert-delay-ms = <200>;

This line alone is also enough!

In short it looks like the delays make the difference and, even a short
delay, can fix the problem.

Of course, regardless of the line-by-line results I also ran with all
the changes so, FWIW:
Tested-by: Daniel Thompson <daniel.thompson@...aro.org>


Daniel.