On Wed, May 02, 2018 at 12:01:53PM +0100, Andre Przywara wrote:

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It looks like there are more users of those power rails, so we could
keep those supplies connected to these fixed regulators here, even with
AXP-805 support in the kernel.

It's not a good choice.

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Or we keep this back until we get proper AXP support in the kernel? I
guess it's quite close to the existing PMICs, so it might be more a
copy&paste exercise to support the AXP-805?

It's not a reason to keep it back.

So I compared the manuals of the AXP806 and the AXP805, the register
interface looks identical to me. I only have a (somewhat) Chinese
version of the AXP806 manual, so couldn't really find the difference
between the two. Do you know more about it? Is it just maybe the
packaging and the electrical properties (like max current supported)?

If the I2C register interface is really the same, we could just add the
DT nodes for the regulator and be done.

And that argument is only valid if you 100% trust the fact that both
datasheet are complete and accurate.

And experience show that you can't.

Well, but I wonder how paranoid we are going to be? And in this case we
have confirmation from Wink that they are the same.

Paranoid enough so that we don't blindly trust that the reviewer had a
coffee, no interruptions or moment of distraction, or that the
datasheet is correct.

But not so paranoid that having the driver running on a kernel is
enough.

So I think we can go with just a DT addition, given that we test it
and confirm that it works for our use case. Should we discover
something odd or undocumented later, I'd consider this a bug fix,
which we then (and only then!) could fix by adding the compatible
string to the driver. Any DT would be fine already, because we list
both compatible strings in there.

In this particular case, yeah, it seems reasonable.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com