Re: [PATCH 01/11] mfd: add the Berlin controller driver

From: Lee Jones
Date: Wed Feb 18 2015 - 10:06:12 EST

On Wed, 18 Feb 2015, Sebastian Hesselbarth wrote:

> On 02/18/2015 12:58 PM, Lee Jones wrote:
> >I do agree that using 'simple-bus' to describe only this IP would be
> >an abuse. However, my foundation thought/argument is unchanged. This
> >'driver' is a hack. It has no functional use besides to work around a
> >problem of semantics and as such has no place in MFD.
> Lee,
> sorry I don't get it. Here you say that using simple-bus is an abuse...
> >Back onto the simple-bus theme, as this is a syscon device it is a bus
> >of sorts. Have you thought about making it a child of your its syscon
> >node, then using simple-bus to get the OF framework to register the
> >child devices?
> ... and here you suggest to use simple-bus to register the child
> devices?

Nope, that's not what I said:

"I do agree that using 'simple-bus' to describe *ONLY THIS IP* would
be an abuse."

... although I believe there is a need to treat syscon devices as
simple buses. There are examples of devices doing this already:

git grep -El 'syscon.*simple-bus' next/master

> I fundamentally disagree that either this registers or syscon in general
> should in any way be seen as a bus. The chip control registers is an
> highly unsorted bunch of bits that we try to match with cleanly
> separated subsystems. This makes it a resource but no bus of any sort.

This is where my comment about semantics comes into play. syscon may
not be a bus is the truest sense; however, this is clearly a
requirement for sub devices to be probed in the same way a simple-bus
is currently. So we're just missing a framework somewhere. We can
fix that.

> The problem that we try to solve here is not a DT problem but solely
> driven by the fact that we need something to register platform_devices
> for pinctrl and reset. The unit we describe in DT is a pinctrl-clock-
> power-reset-unit - or short chip control.

I agree with the last part, but this is a DT problem. It lacks the
functionality to be able to cleanly register these types of
(sub-)devices. Devices which, in my opinion should be described
inside the parent syscon node.

> If you argue that mfd is not the right place for this "driver" we'll
> have to find a different place for it. I remember Mike has no problem
> with extending early probed clock drivers to register additional
> platform_devices - so I guess we end up putting it in there ignoring
> mfd's ability to do it for us.

My argument is not that this fake driver doesn't belong in MFD, it's
that it doesn't belong. That includes shoving it in drivers/clk. I
will be only too happy to have a chat with Mike and provide him with
my reasons why.

What I think we should do however, it write some framework code which
can neatly handle these use-cases, which may just be a case of:


... obviously I'm oversimplifying by quite some margin, but I'm sure
you catch my drift.

Lee Jones
Linaro STMicroelectronics Landing Team Lead â Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at