On Fri, Oct 25, 2019 at 2:07 AM Vaittinen, Matti
[off-list ref] wrote:

Hi Again Jacek,

This has been a nice conversation. I guess I have learned something
from this all but I think this is no longer going forward too much :)
I'll cook up second version - where I add LEDs to DT (even if I don't
see the value for it now). I won't add own compatible for the LED (for
now) - as it is part of MFD - and I'll add the LEDs also to binding
docs. I think that will get the attention from Lee/Rob better than the
LED driver discussion. We can continue discussion there. I hope this is
Ok to you. (And then just few compulsory notes about my view on your
replies - after all, I can't let you to have the final say xD - you can
ignore them or respond just as you like)

On Fri, 2019-10-25 at 00:04 +0200, Jacek Anaszewski wrote:

quoted

Hi Matti,

On 10/24/19 10:15 AM, Vaittinen, Matti wrote:

quoted

Hello Jacek,

On Wed, 2019-10-23 at 23:59 +0200, Jacek Anaszewski wrote:

quoted

On 10/23/19 10:37 AM, Vaittinen, Matti wrote:

quoted

On Tue, 2019-10-22 at 19:40 +0200, Jacek Anaszewski wrote:

quoted

On 10/22/19 2:40 PM, Vaittinen, Matti wrote:

quoted

On Mon, 2019-10-21 at 21:09 +0200, Jacek Anaszewski wrote:

quoted

On 10/21/19 10:00 AM, Vaittinen, Matti wrote:

quoted

Hello Dan,

Thanks for taking the time to check my driver :) I
truly
appreciate
all
the help!

A "fundamental question" regarding these review
comments is
whether
I
should add DT entries for these LEDs or not. I thought
I
shouldn't
but
I would like to get a comment from Rob regarding it.

If the LED controller is a part of MFD device probed from
DT
then
there is no doubt it should have corresponding DT sub-
node.

Agreed.

[...]

quoted

quoted

Right. Or at first it might be enough (and simplest) to assume that
if
LEDs are used via this driver, then colour for both LEDs is set
explicitly by user-space. I wouldn't try guessing if sibling LED
state
changes to OFF when one LED is turned ON - or if LED states change
to
ON if both are turned OFF. This would require exporting interfaces
from
power-supply driver - and it would still be racy. The thing is that
when both LEDs are on board they are both either under HW or SW
control. So it makes no sense to control only one LED in such case.
Thus I think it is Ok if this LED driver is registering both class
devices at one probe. No need to instantiate own platform devices
for
both of the LEDs.

We always register all LEDs originating from the same device in one
probe.

Then I see little benefit from of_compatible or leds subnode for MFD
devices with many LEDs. The driver or core must in any ways parse the
DT in order to find the sub nodes with information for individual LEDs.
I don't think that would be much different from just using the MFD node
as controller node and walking through the MFD child nodes to locate
LED sub nodes (at least for MFDs with simple LED controller).

The cases for not having child nodes are when you have child nodes
with nothing more than a compatible and possibly provider properties
(e.g. #gpio-cells for gpio providers). If you have other resource
dependencies (e.g. clocks) or data to define (e.g. voltages for
regulators), then child nodes absolutely make sense. Once we have
child nodes, then generally it is easier for every function to be a
child node and not mix the two. I'm sure I have told people
incorrectly to not do child nodes because they define incomplete
bindings.

I would group the led nodes under an led-controller node (with a
compatible). The simple reason is each level only has one
number/address space and you can't mix different ones. You're not
numbering the leds here, but could you (with numbers that correspond
to something in the h/w, not just 0..N)? The other reason is modern
LED bindings define a controller node for the controller and led nodes
for the actual led on the board. While the MFD node could be the
controller node, that gets into mixing.

Rob