netdev - Re: [PATCH] net: phy: dp83867: Add support for hardware blinking LEDs

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Date: Sat, 9 Sep 2023 15:20:05 +0200
From: Andrew Lunn <andrew@...n.ch>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Alexander Stein <alexander.stein@...tq-group.com>,
	netdev@...r.kernel.org, Sascha Hauer <s.hauer@...gutronix.de>,
	Heiner Kallweit <hkallweit1@...il.com>,
	linux-kernel@...r.kernel.org, kernel@...gutronix.de,
	Michael Riesch <michael.riesch@...fvision.net>
Subject: Re: [PATCH] net: phy: dp83867: Add support for hardware blinking LEDs

On Sat, Sep 09, 2023 at 08:15:37AM +0100, Russell King (Oracle) wrote:
> On Sat, Sep 09, 2023 at 04:27:31AM +0200, Andrew Lunn wrote:
> > > This works as intended so far. Unfortunately this driver and the PHY LED 
> > > framework do not support active-low LEDs (yet).
> > 
> > Polarity is something which i've seen a few PHY devices have. It also
> > seems like a core LED concept, not something specific to PHY LEDs. So
> > i think this needs to be partially addressed in the LED core.
> 
> However, doesn't the LED layer deals with LED brightness, not by logic
> state? It certainly looks that way, and it's left up to the drivers
> themselves to deal with any polarity inversion - which makes sense if
> the core is just concerned about brightness.
> 
> Introducing inversion in the core means drivers will be passed a
> brightness of "100" for off and "0" for on which, do you not think,
> starts to get rather silly?

Documentation/devicetree/bindings/leds/leds-pwm.yaml has:

      active-low:
        description:
          For PWMs where the LED is wired to supply rather than ground.
        type: boolean

leds-pwm-multicolor.yaml and leds-bcm6358.txt uses the same
property. There is also one case of: irled/ir-spi-led.yaml

  led-active-low:
    type: boolean
    description:
      Output is negated with a NOT gate.

The implementation of the properties is repeated in each driver. So we
probably need to add the parsing of this property in phy_device.c, and
add a led_config() op to struct phy_device to pass polarity
information to the driver.

	Andrew