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Message-ID: <aBxtgZw6+BM36Rru@duo.ucw.cz>
Date: Thu, 8 May 2025 10:38:25 +0200
From: Pavel Machek <pavel@....cz>
To: Nam Tran <trannamatk@...il.com>
Cc: andy@...nel.org, geert@...ux-m68k.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.
>
> The LP5812 is used for LED status indication in devices like smart speakers,
> wearables, and routers, not as a structured rectangular display.
Show us one device where it is used, photo would be best. I suspect
that the router use might indeed qualify for LED subsystem.
You described is at 4x3 display, but it is really used as 4xRGB?
> Given that, it seems to match the LED subsystem better than auxdisplay, doesn't it?
Seems so, yes. From description, I assumed it was 4x3xRGB, not 4xRGB.
Best regards,
Pavel
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