linux-kernel - Re: [RESEND PATCH v6 2/3] leds: Add driver for the TLC5925 LED controller

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Message-ID: <CAHp75Ve9tug8HzYXx+9HU09=Bae+=M24HwH1n1XOpL=RsUOpQw@mail.gmail.com>
Date:   Thu, 4 Aug 2022 22:40:44 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jean-Jacques Hiblot <jjhiblot@...phandler.com>
Cc:     Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v6 2/3] leds: Add driver for the TLC5925 LED controller

On Thu, Aug 4, 2022 at 10:23 PM Jean-Jacques Hiblot
<jjhiblot@...phandler.com> wrote:
> On 31/07/2022 21:28, Andy Shevchenko wrote:
> > On Fri, Jul 22, 2022 at 10:14 AM Jean-Jacques Hiblot
> > <jjhiblot@...phandler.com> wrote:
> >> The TLC5925 is a 16-channels constant-current LED sink driver.
> >> It is controlled via SPI but doesn't offer a register-based interface.
> >> Instead it contains a shift register and latches that convert the
> >> serial input into a parallel output.
> >>
> >> Datasheet: https://www.ti.com/lit/ds/symlink/tlc5925.pdf
> >> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...phandler.com>
> >> Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> > Sorry for my slowpokeness, but I just realized that this driver may
> > not be needed. What is the difference to existing gpio-74x164?
>
> It might work. However it might not be as practical and efficient as the
> dedicated LED driver.

I'm not sure what efficiency you are talking about? Using LED GPIO +
GPIO? But the chip, even if marketed as an LED driver, might be used
not for LEDs, right? Technically speaking it's a GPIO with powerful
(by current sink) outputs. With LED + GPIO you get flexibility to
configure and describe your system exactly how it is designed on the
PCB level.

Note, we have already examples of other chips (like PWM) being used as
GPIO. In different cases in Linux we have different approaches on how
to solve that. In general, Linux kernel pin control misses some
special functions of the pins that may be assigned to them, while
being a simple pin control (or even GPIO expander).

> I'll give a try.

Thanks!

-- 
With Best Regards,
Andy Shevchenko