netdev - Re: [RFC PATCH v4 0/8] Adds support for PHY LEDs with offload triggers

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Date:   Fri, 12 Nov 2021 16:35:21 +0100
From:   Ansuel Smith <ansuelsmth@...il.com>
To:     Marek Behún <kabel@...nel.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jonathan Corbet <corbet@....net>, Pavel Machek <pavel@....cz>,
        John Crispin <john@...ozen.org>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: [RFC PATCH v4 0/8] Adds support for PHY LEDs with offload
 triggers

On Thu, Nov 11, 2021 at 03:16:08AM +0100, Marek Behún wrote:
> On Thu, 11 Nov 2021 02:34:52 +0100
> Ansuel Smith <ansuelsmth@...il.com> wrote:
> 
> > This is another attempt in adding support for PHY LEDs. Most of the
> > times Switch/PHY have connected multiple LEDs that are controlled by HW
> > based on some rules/event. Currently we lack any support for a generic
> > way to control the HW part and normally we either never implement the
> > feature or only add control for brightness or hw blink.
> > 
> > This is based on Marek idea of providing some API to cled but use a
> > different implementation that in theory should be more generilized.
> > 
> > The current idea is:
> > - LED driver implement 3 API (hw_control_status/start/stop).
> >   They are used to put the LED in hardware mode and to configure the
> >   various trigger.
> > - We have hardware triggers that are used to expose to userspace the
> >   supported hardware mode and set the hardware mode on trigger
> >   activation.
> > - We can also have triggers that both support hardware and software mode.
> > - The LED driver will declare each supported hardware blink mode and
> >   communicate with the trigger all the supported blink modes that will
> >   be available by sysfs.
> > - A trigger will use blink_set to configure the blink mode to active
> >   in hardware mode.
> > - On hardware trigger activation, only the hardware mode is enabled but
> >   the blink modes are not configured. The LED driver should reset any
> >   link mode active by default.
> > 
> > Each LED driver will have to declare explicit support for the offload
> > trigger (or return not supported error code) as we the trigger_data that
> > the LED driver will elaborate and understand what is referring to (based
> > on the current active trigger).
> > 
> > I posted a user for this new implementation that will benefit from this
> > and will add a big feature to it. Currently qca8k can have up to 3 LEDs
> > connected to each PHY port and we have some device that have only one of
> > them connected and the default configuration won't work for that.
> > 
> > I also posted the netdev trigger expanded with the hardware support.
> > 
> > More polish is required but this is just to understand if I'm taking
> > the correct path with this implementation hoping we find a correct
> > implementation and we start working on the ""small details""
> 
> Hello Ansuel,
> 
> besides other things, I am still against the idea of the
> `hardware-phy-activity` trigger: I think that if the user wants the LED
> to indicate network device's link status or activity, it should always
> be done via the existing netdev trigger, and with that trigger only.
> 
> Yes, I know that netdev trigger does not currently support indicating
> different link modes, only whether the link is up (in any mode). That
> should be solved by extending the netdev trigger.
> 
> I am going to try to revive my last attempt and send my proposal again.
> Hope you don't mind.
> 
> Marek

Honestly... It's a bit sad.
The netdev trigger have its limitation and I see introducing an
additional trigger a practical way to correctly support some
strange/specific PHY.
I implemented both idea: expand netdev and introduce a dedicated
trigger and still this is problematic.
Is having an additional trigger for the specific task that bad?

I don't care as long as the feature is implemented but again
pretty sad how this LEDs proposal went.

-- 
	Ansuel