Re: [PATCH v3 04/12] dt-bindings: timer: arm,arch_timer: Add optional clock and reset

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Hi Rob,

On Thu, May 5, 2022 at 12:33 AM Rob Herring <robh@xxxxxxxxxx> wrote:
> On Tue, May 03, 2022 at 02:11:59PM +0100, Mark Rutland wrote:
> > This is the only patch from this series that I've received, and judging
> > by the CC list this hasn't gone to either LKML or LAKML, so I'm missing
> > the surrounding context for this.
> >
> > Looking on lore, this is part of:
> >
> >   https://lore.kernel.org/linux-devicetree/20220503115557.53370-1-phil.edworthy@xxxxxxxxxxx/T/#t
> >
> > ... which is adding support for an arm64 SoC.
> >
> > On Tue, May 03, 2022 at 12:55:49PM +0100, Phil Edworthy wrote:
> > > Some SoCs use a gated clock for the timer and the means to reset the timer.
> > > Hence add these as optional.
> >
> > The clock feeding the architected timer is supposed to be in an
> > always-on clock domain, and is supopsed to be enabled before running any
> > Normal World software.
> >
> > The arm64 kernel *requires* that this is enabled prior to entry. If the
> > kernel ever has to touch either the clock or reset, then there are
> > phases where the counter will not function correctly, which is simply
> > broken.
> >
> > Given that, I do not think this should be in the DT, and instead the
> > clock should be marked as critical in the provider node (and the reset
> > should never be touched).
>
> That is not yet an accepted DT property, but is currently on the list
> for review[1]. If that's something people need, chime in. More than 1
> person needing something is always better.

I am aware of[1]. AFAIU, that is meant for clocks that need to stay
enabled for external reasons (external hardware driven by on-SoC
clock).
For internal reasons (e.g. arch-timer), CLK_IS_CRITICAL is fine.

> [1] https://lore.kernel.org/all/20220428110107.149524-1-marex@xxxxxxx/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds



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