Re: [PATCH net-next 5/5] igc: Export LEDs

[Heiner Kallweit <hkallweit1@gmail.com>]

On 29.07.2021 10:59, Marek Behún wrote:
> Hello Heiner,
> 
> On Wed, 28 Jul 2021 22:43:30 +0200
> Heiner Kallweit <hkallweit1@gmail.com> wrote:
> 
>> Did we come to any conclusion?
>>
>> My preliminary r8169 implementation now creates the following LED names:
>>
>> lrwxrwxrwx 1 root root 0 Jul 26 22:50 r8169-led0-0300 -> ../../devices/pci0000:00/0000:00:1d.0/0000:03:00.0/net/enp3s0/r8169-led0-0300
>> lrwxrwxrwx 1 root root 0 Jul 26 22:50 r8169-led1-0300 -> ../../devices/pci0000:00/0000:00:1d.0/0000:03:00.0/net/enp3s0/r8169-led1-0300
>> lrwxrwxrwx 1 root root 0 Jul 26 22:50 r8169-led2-0300 -> ../../devices/pci0000:00/0000:00:1d.0/0000:03:00.0/net/enp3s0/r8169-led2-0300
>>
>> I understood that LEDs should at least be renamed to r8169-0300::link-0
>> to link-2 Is this correct? Or do we have to wait with any network LED support
>> for a name discussion outcome?
> 
> I would expect some of the LEDs to, by default, indicate activity.
> So maybe look at the settings BIOS left, and if the setting is to
> indicate link, use the "link" function, and if activity, use the
> "activity" function? 
> 

The function may be changed by the user. Then what? Rename the LED device?
A typical use case is also that one LED indicates both, link and activity.

>> For the different LED modes I defined private hw triggers (using trigger_type
>> to make the triggers usable with r8169 LEDs only). The trigger attribute now
>> looks like this:
>>
>> [none] link_10_100 link_1000 link_10_100_1000 link_ACT link_10_100_ACT link_1000_ACT link_10_100_1000_ACT
>>
>> Nice, or? Issue is just that these trigger names really should be made a
>> standard for all network LEDs. I don't care about the exact naming, important
>> is just that trigger names are the same, no matter whether it's about a r8169-
>> or igc- or whatever network chip controlled LEDs.
> 
> This is how I at first proposed doing this, last year. But this is
> WRONG!
> 
> First, we do not want a different trigger for each possible
> configuration. We want one trigger, and then choose configuration via
> other sysfs file. I.e. a "hw" trigger, which, when activated, would
> create sysfs files "link" and "act", via which you can configure those
> options.
> 
> Second, we already have a standard LED trigger for network devices,
> netdev! So what we should do is use the netdev trigger, and offload
> blinking to the LED controller if it supports it. The problems with
> this are:
> 1. not yet implemented in upstream, see my latest version
>    https://lore.kernel.org/linux-leds/20210601005155.27997-1-kabel@kernel.org/
> 2. netdev trigger currently does not support all these different link
>    functions. We have these settings:
>      device_name: network interface name, i.e. eth0
>      link: 0 - do not indicate link
>            1 - indicate link (ON when linked)
>      tx: 0 - do not blink on transmit
>          1 - blink on transmit
>      rx: 0 - do not blink on receive
>          1 - blink on receive
>      interval: duration of LED blink in ms
> 
> I would like to extend netdev trigger to support different
> configurations. Currently my ideas are as follows:
> - a new sysfs file, "advanced", will show up when netdev trigger is
>   enabled (and if support is compiled in)
> - when advanced is set to 1, for each possible link mode (10base-t,
>   100base-t, 1000base-t, ...) a new sysfs directory will show up, and

This leads to new questions like: How do you know what the possible
link modes are? In a spare minute you could have a look at enum
ethtool_link_mode_bit_indices. Even with standard multi-gig hw
meanwhile you have: 10M, 100M, 1G, 2.5G, 5G, 10G.
Supposedly the information about possible link modes would have to be
stored in led_classdev so that it can generate the appropriate sysfs
directories during registration.

>   in each of these directories the following files:
>     rx, tx, link, interval, brightness
>     multi_intensity (if the LED is a multi-color LED)
>   and possibly even
>     pattern
> With this, the user can configure more complicated configurations:
> - different LED color for different link speeds
> - different blink speed for different link speeds
> And if some of the configurations are offloadable to the HW, the drivers
> can be written to support such offloading. (Maybe even add a read-only
> file "offloaded" to indicate if the trigger was offloaded.)
> 

For a fully hw-offloaded LED like in my case then more or less the only
benefit of led_classdev + netdev trigger is the unified location of
link speed + tx/rx attributes. The brightness attribute has no meaning
because brightness can't be controlled.
Overall quite some overhead for a small functionality. At least in a
simple case like mine I'd use custom attributes under the net_dev like
this if I had to invent something on my own:
led0/speed: where you can say: "echo +100 > led0/speed" to enable 100M link indication
led0/activity: bool

> I will work on these ideas in the following weeks and will sent
> proposals to linux-leds.
> 

I don't want to be the one always saying: Nice framework, but heh:
How about my special case xyz?

I understand that it can be a frustrating job, that needs quite some
patience, to create a framework that you consider to be clean and
that covers the needs of (almost) everybody. I failed with some early
attempts to establish RGB LED support using the HSV color model.

>> And I don't have a good solution for initialization yet. LED mode is whatever
>> BIOS sets, but initial trigger value is "none". I would have to read the
>> initial LED control register values, iterate over the triggers to find the
>> matching one, and call led_trigger_set() to properly set this trigger as
>> current trigger.
> 
> You can set led_cdev->default_trigger prior registering the LED. But
> this is moot: we do not want a different trigger for each PHY interface
> mode.
> 
> Marek
>