linux-kernel - Re: [PATCH v5 7/7] Input: matrix_keypad

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Message-ID: <Z71qEyDVz22j_CvL@google.com>
Date: Mon, 24 Feb 2025 22:58:27 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Manuel Traut <manuel.traut@...com>
Cc: Markus Burri <markus.burri@...com>, linux-kernel@...r.kernel.org,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Marek Vasut <marek.vasut@...il.com>, linux-input@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v5 7/7] Input: matrix_keypad - detect change during scan

On Wed, Feb 19, 2025 at 05:56:10PM +0100, Manuel Traut wrote:
> On Fri, Jan 10, 2025 at 06:49:06AM +0100, Markus Burri wrote:
> > For a setup where the matrix keypad is connected over a slow interface
> > (e.g. a gpio-expansion over i2c), the scan can take a longer time to read.
> > 
> > Interrupts need to be disabled during scan. And therefore changes in this
> > period are not detected.
> > To improve this situation, scan the matrix again if the row state changed
> > during interrupts disabled.
> > The rescan is repeated until no change is detected anymore.
> 
> This is a quirk for a bad hardware design. For 'good' hardware it adds
> an additional read_row_state for no need. For even slower connected
> GPIOs this will also not help much. However it is obvious that it will
> be an improvement for some designs. 
> 
> Dmitry, would it make sense to make this configurable?

What if we do not disable interrupts after the first one, but record
the last interrupt time and rescan if it arrived after work handler
started executing?

Thanks.

-- 
Dmitry