On Wed, Aug 27, 2014 at 05:42:21PM +0200, Maxime Ripard wrote:

On Wed, Aug 27, 2014 at 11:52:48AM +0200, Thierry Reding wrote:

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On Wed, Aug 27, 2014 at 10:45:26AM +0200, Maxime Ripard wrote:

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On Wed, Aug 27, 2014 at 08:54:41AM +0200, Thierry Reding wrote:

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On Tue, Aug 26, 2014 at 11:02:48PM +0200, Maxime Ripard wrote:

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On Tue, Aug 26, 2014 at 04:35:51PM +0200, Thierry Reding wrote:

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Mike Turquette repeatedly said that he was against such a DT property:
https://lkml.org/lkml/2014/5/12/693

Mike says in that email that he's opposing the addition of a property
for clocks that is the equivalent of regulator-always-on. That's not
what this is about. If at all it'd be a property to mark a clock that
should not be disabled by default because it's essential.

It's just semantic. How is "a clock that should not be disabled by
default because it's essential" not a clock that stays always on?

Because a clock that should not be disabled by default can be turned off
when appropriate. A clock that is always on can't be turned off.

If a clock is essential, then it should never be disabled. Or we don't
share the same meaning of essential.

Essential for the particular use-case.

So, how would the clock driver would know about which use case we're
in? How would it know about which display engine is currently running?
How would it know about which video output is being set?

Currently, we have two separate display engines, which can each output
either to 4 different outputs (HDMI, RGB/LVDS, 2 DSI). Each and every
one of these combinations would require different clocks. What clocks
will we put in the driver? All of them?

Ideally the solution wouldn't involve hard-coding this into the clock
driver at all. There should be a way for firmware to communicate to the
kernel that a given clock shouldn't be disabled. Then since firmware
already knows what it set up it can tell the kernel to not touch those.

Thierry
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