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

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Message-Id: <20250428172917.25405-1-trannamatk@gmail.com>
Date: Tue, 29 Apr 2025 00:29:17 +0700
From: Nam Tran <trannamatk@...il.com>
To: geert@...ux-m68k.org,
	pavel@....cz
Cc: andy@...nel.org,
	robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org,
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	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v8 0/5] auxdisplay: add support for TI LP5812 4x3 Matrix LED driver

Hi Geert, Pavel,

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:

> Hi Pavel,
> 
> On Mon, 28 Apr 2025 at 12:37, Pavel Machek <pavel@....cz> wrote:
> > > > This patch series adds support for the TI/National Semiconductor LP5812
> > > > 4x3 matrix RGB LED driver. The driver supports features such as autonomous
> > > > animation and time-cross-multiplexing (TCM) for dynamic LED effects.
> > > >
> > > > Signed-off-by: Nam Tran <trannamatk@...il.com>
> > > > ---
> > > > Changes in v8:
> > > > - 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.

Best regards,
Nam Tran