linux-kernel - Re: [PATCH v8 0/5] auxdisplay: add support for TI LP5812 4x3 Matrix LED driver

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Message-ID: <aA/ineUBAM5IU79J@duo.ucw.cz>
Date: Mon, 28 Apr 2025 22:18:37 +0200
From: Pavel Machek <pavel@....cz>
To: Nam Tran <trannamatk@...il.com>
Cc: geert@...ux-m68k.org, andy@...nel.org, robh@...nel.org,
	krzk+dt@...nel.org, conor+dt@...nel.org,
	christophe.jaillet@...adoo.fr, corbet@....net,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, florian.fainelli@...adcom.com,
	bcm-kernel-feedback-list@...adcom.com,
	linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v8 0/5] auxdisplay: add support for TI LP5812 4x3 Matrix
 LED driver

Hi!

> Thank you, Pavel, for the confirmation.
> Thank you, Geert, for the review and the question.
> 
> I would like to make it clearer.
> 
> On Mon, 28 Apr 2025 Geert Uytterhoeven wrote:
> 

> > > > > - Move driver to drivers/auxdisplay/ instead of drivers/leds/.
> > > > > - Rename files from leds-lp5812.c/.h to lp5812.c/.h.
> > > > > - Move ti,lp5812.yaml binding to auxdisplay/ directory,
> > > > >   and update the title and $id to match new path.
> > > > > - No functional changes to the binding itself (keep Reviewed-by).
> > > > > - Update commit messages and patch titles to reflect the move.
> > > > > - Link to v7: https://lore.kernel.org/linux-leds/20250422190121.46839-1-trannamatk@gmail.com/
> > > >
> > > > Out of sudden without discussing with auxdisplay maintainers/reviewers?
> > > > Thanks, no.
> > > > Please, put into the cover letter the meaningful summary of what's
> > > > going on and why this becomes an auxdisplay issue. Brief review of the
> > > > bindings sounds more likely like LEDS or PWM subsystems.
> > >
> > > It is 4x3 matrix. That means it is not suitable for LEDs. I don't
> > > believe it is suitable for PWM, either -- yes, it is 36 PWM outputs,
> > > but...
> > 
> > Is it intended to be used as a 4x3 matrix, or is this just an internal
> > wiring detail, and should it be exposed as 12 individual LEDs instead?
> 
> The 4×3 matrix is a real and fundamental aspect of the LP5812’s operation.
> It is not just an internal wiring detail.
> The device adopts a Time-Cross-Multiplexing (TCM) structure, where 4 output
> pins control 12 LED dots individually through scanning. Each pin includes
> both high-side and low-side drive circuits, meaning matrix multiplexing is
> required for proper operation — it cannot be treated as 12 completely
> independent LEDs.

Scanning is really a detail.

If this is used as rectangular 4x3 display, then it goes to auxdisplay.

If this is used as a power LED, SD activity LED, capslock and numlock
... placed randomly all around the device, then it goes LED subsystem.

Best regards,
								Pavel
-- 
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