Re: [PATCH] net: phy: at803x: Add support to control PHY LEDs

On Mon, Mar 21, 2016 at 06:36:50PM +0100, Vishal Thanki wrote:

Hi,

On Thu, Mar 17, 2016 at 07:07:12PM +0100, Vishal Thanki wrote:

quoted

quoted

They might not be on/off controllable individually, but you can often
set them to show Packet RX, Packet TX, Link, speed, etc, in a
reasonably flexible way. So you could have LED triggers mapping to
these functionalities. The user can then pick the trigger for the LED.

Actually, the data sheet says:

2.3.4 LED Interface

The LED interface can either be controlled by the PHY or controlled
manually, independent of the state of the PHY. Two status LEDs are
available. These can be used to indicate operation speed, and link
status. The LEDs can be programmed to different status functions from
their default value. They can also be controlled directly from the MII
register interface.

So maybe you can control the on/off state.

I need some more understanding on using the LED subsystem for this task.
Pardon my lack of knowledge, and probably silly questions too.

Here is what I understood when we decide to use the LED subsystem for
exposing PHY LEDs.

1) Have a generic driver under drivers/leds/, for example leds-eth-phy.c
2) Implement a set of phylib APIs which will be used by generic phy led
driver to set the brightness.
3) The phylib APIs will depend on actual PHY driver, at803x.c for
example, (by means of callbacks implemented in PHY driver) to control LEDs.
4) PHY driver can advertise its support for LEDs using the capability
flags.

Please let me know if my understanding is correct.

LEDs are more than brightness. They can also have triggers.

It would require some rework of the LED core, but you could imagine
being able to associate triggers to specific LEDs. You could have
triggers like "eth-phy-link" and "eth-phy-activity" which the phylib and
phy driver exports. The PHY would export LEDs and say that they can be
used with these triggers. So when for example the "eth-phy-link"
trigger is activated on an LED, the PHY driver programs the hardware
to show the link status on the LED.

The key here is that the hardware is in control of the LED, when the
trigger is used. You don't want software involved when you are
transmitting a million packets per second.

	Andrew