Re: [PATCH 2/2 v4] clk: Add Gemini SoC clock controller

[Stephen Boyd <sboyd@codeaurora.org>]

On 06/12, Linus Walleij wrote:
> On Thu, Jun 8, 2017 at 2:18 PM, Linus Walleij <linus.walleij@linaro.org> wrote:
> 
> > I think the timer may be more of an issue...
> >
> > It is using CLOCKSOURCE_OF_DECLARE(), at least last time
> > I checked there was no such thing as clocksources retrying their
> > calls, and that cannot be regular probes because of, yeah device
> > core is using the timer, I think.
> >
> > Yeah I looked in:
> > drivers/clocksource/clksrc-probe.c
> >
> > It will just fail if it can't initialize the clocksource.
> >
> > I don't understand what platforms can actually get their timers
> > up at all without the clock framework? Those hardcoding the
> > clock frequency in the device tree, or things like the ARM
> > TWD which has it encoded in hardware perhaps?
> 
> I just confirmed this to be the problem using a scratch patch for
> a platform device init and some earlydebug prints:
> 
> Uncompressing Linux... done, booting the kernel.
>  Booting Linux on physical CPU 0x0
> start_kernel
> (...)
>  NR_IRQS:16 nr_irqs:16 16
>  could not get PCLK
> Failed to initialize '/soc/timer@43000000': -517
>  clocksource_probe: no matching clocksources found
>  sched_clock: 32 bits at 100 Hz, resolution 10000000ns, wraps every
> 21474836475000000ns
>  Console: colour dummy device 80x30
>  Calibrating delay loop...
> 
> So the deferred clock makes the whole platform hang because the timer
> needs it. Without a clocksource, the delay loop cannot be calibrated, so
> it hangs there.
> 

Ok. So can the certain clks that are required to get the timer
going be put into CLK_OF_DECLARE_DRIVER() and then have a regular
platform driver for the rest of the clks that aren't required for
early boot? We've been doing this sort of hybrid design lately,
so hopefully that works here too.

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