Re: [PATCH v3] clk: exynos5420: Remove aclk66_peric from the clock tree description

Quoting Doug Anderson (2014-06-05 17:46:23)

Mike,

On Thu, Jun 5, 2014 at 5:03 PM, Mike Turquette [off-list ref] wrote:

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Quoting Doug Anderson (2014-06-05 13:35:14)

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The "aclk66_peric" clock is a gate clock with a whole bunch of gates
underneath it.  This big gate isn't very useful to include in our
clock tree.  If any of the children need to be turned on then the big
gate will need to be on anyway.  ...and there are plenty of other "big
gates" that aren't described in our clock tree, some of which shut off
collections of clocks that have no relationship in the hierarchy so
are hard to model.

I think this is a common problem. On OMAP we have something similar to
this called "clock domains" or "clkdm" and it has been historically
handled outside of the Linux clock framework[1]. There is a relationship
to the clock framework of course and in the future it might be
worthwhile to see if there is a generic way to handle this stuff.

That sounds like something that would be nice to solve, but it's not
going to happen now.

On the off chance that the user manual mentioned the existence of one
of these "big gate" bits, it tends to not be very specific about
_exactly_ which sets of clocks it disables.

Tracking down every one of these would be hugely time consuming.
Also: as Tomasz has indicated they don't provide a huge amount of
benefit since we're already dealing with clocks on a more fine-grained
level...

Sounds like you are dealing with crappy documentation :-(

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"aclk66_peric" is causing earlyprintk problems since it gets disabled
as part of the boot process, so let's just remove it.

Strangely (and for no good reason) this clock is exported as part of
the common clock bindings.  Remove it since there are no in-kernel
device trees using it and no reason anyone out of tree should refer to
it either.

So Linux has no control over the big gate now, correct? You are
dependent on the bootloader to ungate this thing?

A better way to put it is that you're dependent on the bootloader not
to gate it.

...but that's also true for pretty much any clock marked IGNORE_UNUSED
and not explicitly enabled anywhere.


Are you opposed to this landing as-is to unblock things and people can
continue to work on the clock driver to make it even better?

No. I'm just trying to understand how things work so that we can arrive
to the right decision. I know what it is like to try and quickly unblock
everyone else and the rush to do so often leads to less awesome
solutions.

Anyways, getting back on point, Tomasz was right about the whole clk_get
thing. So I'm happy to take either V1 or V3 of your patch. I will be
submitting a second PR for 3.16 next week and it will include whichever
version you and Tomasz agree is best.

Regards,
Mike

-Doug