linux-kernel - Re: [PATCH v3 2/3] leds: add support for TI LP5860 LED driver chip

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <87ldkjip1t.fsf@pengutronix.de>
Date: Thu, 06 Nov 2025 08:43:42 +0100
From: Steffen Trumtrar <s.trumtrar@...gutronix.de>
To: Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc: Lee Jones <lee@...nel.org>,  Pavel Machek <pavel@....cz>,  Rob Herring
 <robh@...nel.org>,  Krzysztof Kozlowski <krzk+dt@...nel.org>,  Conor
 Dooley <conor+dt@...nel.org>,  Steffen Trumtrar <kernel@...gutronix.de>,
  Pavel Machek <pavel@...nel.org>,  Mark Brown <broonie@...nel.org>,
  linux-leds@...r.kernel.org,  devicetree@...r.kernel.org,
  linux-spi@...r.kernel.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] leds: add support for TI LP5860 LED driver chip


Hi Jacek,

On 2025-10-11 at 15:09 +02, Jacek Anaszewski <jacek.anaszewski@...il.com> wrote:

> Hi Steffen
> 
> On 9/30/25 09:40, Steffen Trumtrar wrote:
> > Hi,
> > On 2025-09-16 at 16:34 +01, Lee Jones <lee@...nel.org> wrote:
> > 
> >> > +#include <linux/gpio.h>
> >> > +#include <linux/led-class-multicolor.h>
> >> > +#include <linux/module.h>
> >> > +#include <linux/of_gpio.h>
> >> > +#include <linux/of_platform.h>
> >> > +#include <linux/regmap.h>
> >> > +
> >> > +#include <linux/platform_data/leds-lp5860.h>
> >> > +
> >> > +static struct lp5860_led *mcled_cdev_to_led(struct led_classdev_mc
> >> *mc_cdev)
> >> > +{
> >> > +    return container_of(mc_cdev, struct lp5860_led, mc_cdev);
> >> > +}
> >> > +
> >> > +LP5860_SHOW_MODE(r_global_brightness_set, LP5860_REG_R_CURRENT_SET,
> >> LP5860_CC_GROUP_MASK, 0)
> >> > +LP5860_STORE_MODE(r_global_brightness_set, LP5860_REG_R_CURRENT_SET,
> >> LP5860_CC_GROUP_MASK, 0)
> >> > +DEVICE_ATTR_RW(r_global_brightness_set);
> >>
> >> How is this different to /sys/class/leds/<led>/multi_intensity?
> >>
> >> # echo 43 226 138 > /sys/class/leds/multicolor:status/multi_intensity
> >> red -
> >>     intensity = 138
> >>     max_brightness = 255
> >> green -
> >>     intensity = 43
> >>     max_brightness = 255
> >> blue -
> >>     intensity = 226
> >>     max_brightness = 255
> >>
> > the LP5860 has a register for setting the maximal brightness that holds for
> > all LEDs in the matrix. multi_intensity and max_brightness is only for that
> > one multicolor LED, right? And I can only manipulate the max_brightness of
> > that one multicolor LED instance.
> > If I'm wrong, I'd be happy to not have to add the sysfs files.
> 
> It seems that this device is similar in the aspect of LED grouping
> to LP50xx family. There is already a driver for that one [0] with
> related bindings. Grouping solution could be addressed similarly to the
> banking mechanism in that driver.
>
> That of course means that this patch needs a significant rework.
> 
> First thing that strikes me after analyzing datasheet is that
> LEDs are not assigned to any group since LP5860_REG_GRP_SEL_START
> address is not referenced anywhere, and this is base address for
> Dot_grp_selN registers that enable affiliation of the LED to given
> group. No need for global brightness setting then.
>

The (now called) global_brightness sets the current of the three color groups respectively. These groups have a fixed mapping:

Group 1 is CS0, CS3, CS6,...
Group 2 is CS1, CS4, CS7,...
Group 3 is CS2, CS5, CS8,...

therefore setting the R, G and B channel. No need to assign any groups for that.

> Anyway, I'd add proper support for this device with DT knobs
> to enable both grouping and individual approach to controlling the LEDs.
> 

As far as I can tell, both drivers are pretty similar already regarding the DT description and setup.

I will just remove the global_brightness (aka global current in the datasheet) stuff, as I don't see that it is really, really needed alas the chip supports this feature and just use the intensity and max_brightness knobs that are already there via the multicolor classdev.


Best regards,
Steffen

-- 
Pengutronix e.K.                | Dipl.-Inform. Steffen Trumtrar |
Steuerwalder Str. 21            | https://www.pengutronix.de/    |
31137 Hildesheim, Germany       | Phone: +49-5121-206917-0       |
Amtsgericht Hildesheim, HRA 2686| Fax:   +49-5121-206917-5555    |