linux-kernel - Re: [PATCH v2] HID: i2c-hid: wait for i2c touchpad deep-sleep to power-up transition

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Message-ID: <ZhzuoWgA88CeenMC@hovoldconsulting.com>
Date: Mon, 15 Apr 2024 11:08:49 +0200
From: Johan Hovold <johan@...nel.org>
To: Łukasz Majczak <lma@...omium.org>
Cc: Jiri Kosina <jikos@...nel.org>, Dmitry Torokhov <dtor@...omium.org>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Douglas Anderson <dianders@...omium.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Maxime Ripard <mripard@...nel.org>,
	Kai-Heng Feng <kai.heng.feng@...onical.com>,
	Johan Hovold <johan+linaro@...nel.org>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, Radoslaw Biernacki <rad@...omium.org>
Subject: Re: [PATCH v2] HID: i2c-hid: wait for i2c touchpad deep-sleep to
 power-up transition

On Thu, Apr 11, 2024 at 04:23:27PM +0200, Łukasz Majczak wrote:
> > Sure, but what about other transactions that are initiated by the host
> > (e.g. SET_POWER)?
> >
> Somehow it is problematic only on reboot and works just fine on
> suspend/resume and
> set_power.
> I will dig more and try to find out what the difference is.

Sounds like it may be related to the i2c_hid_set_power() on shutdown()
then as Kai-Heng pointed out.

That function already handles a similar retry for I2C_HID_PWR_ON during
resume.

> > Perhaps this hack at probe is enough for your use case, but is an
> > incomplete hack and at a minimum you'd need to add a comment explaining
> > why it is there.
> >
> You mean a comment in the code ?

Yes, if this turns out to be needed then there should be a comment
explaining why it is there (and currently also as the delays you used
seem specific for your particular platform).

But hopefully you can find a generic solution to this.

Johan