Re: [PATCH 3/3] clk: Provide OF helper to mark clocks as CRITICAL

[Lee Jones]

On Tue, 02 Feb 2016, Andre Przywara wrote:

> Hi Maxime,
> 
> On 01/02/16 06:32, Maxime Ripard wrote:
> > Hi Andre,
> > 
> > On Wed, Jan 27, 2016 at 11:51:45PM +0000, Andrà Przywara wrote:
> >> Hi,
> >>
> >> On 18/01/16 14:28, Lee Jones wrote:
> >>> This call matches clocks which have been marked as critical in DT
> >>> and sets the appropriate flag.  These flags can then be used to
> >>> mark the clock core flags appropriately prior to registration.
> >>
> >> I like the idea of having a generic property very much. Also this solves
> >> a problem I have in a very elegant way.
> > 
> > Not really. It has a significant set of drawbacks that we already
> > detailed in the initial thread, which are mostly related to the fact
> > that the clocks are to be left on is something that totally depends on
> > the software support in the kernel. Some clocks should be reported as
> > critical because they are simply missing a driver for it, some should
> > be because the driver for it as not been compiled, some should because
> > we don't have the proper clocks drivers yet for one of their
> > downstream clocks.
> > 
> > Basically, it all boils down to this: some clocks should never ever be
> > shutdown because <hardware reason>, and I believe it's the case Lee is
> > in. But most of the current code that would use it might, and might
> > even need at some point to shut down such a clock.
> 
> I was bascically interested in pushing the critical-clock property into
> DT to solve that cumbersome clk-sunxi init scheme - which you have fixed
> now in a much better way (thanks for that, btw.)
> For that particular case the CPU clock really looks like being actually
> critical in the hardware sense - no-one maybe except the mgmt core
> should turn the one single CPU clock source off.
> 
> So I wonder if we should document this "for hardware reasons only" and
> still have that property in DT?
> At the weekend I coded something into the generic DT clock code to let
> it parse for basically every clock node - without a particular driver
> needing to ask for it.
> If this sounds useful to you I can post that one.

It sounds very useful.  Very useful indeed.  But then I would say
that, because that's how this all started in the first place: ;)

  https://lkml.org/lkml/2015/7/22/299

I still think it's a pretty elegant method, but it was NACKed by Mike.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org â Open source software for ARM SoCs
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