[U-Boot] [PATCH] timer: Add High Precision Event Timers (HPET) support

[Ivan Gorinov]

On Thu, Mar 29, 2018 at 01:52:10PM +0300, Andy Shevchenko wrote:
> On Wed, 2018-03-28 at 17:58 -0700, Ivan Gorinov wrote:
> > Adding HPET as an alternative timer for x86 (default is TSC).
> > HPET main counter has constant clock frequency, calibration is not
> > required.
> > This change also makes TSC timer driver optional on x86 platforms.
> > If X86_TSC is disabled, early timer functions are provided by HPET.
> > 
> > HPET can be selected as the tick timer in the Device Tree "chosen"
> > node:
> > 
> >   /include/ "hpet.dtsi"
> > 
> >   chosen {
> >     tick-timer = "/hpet0";
> >   };
> 
> First question is how this will work in case of Broadwell and Ivybridge
> that have something to do with HPET in their CPU code, i.e.
> 
> arch/x86/cpu/broadwell/pch.c
> arch/x86/cpu/ivybridge/lpc.c

The platform-specific code maps HPET registers to make sure they are
available to the timer driver added by this patch.

Apparently, HPET is also used by the DRAM initialization code (MRC)
on Ivy Bridge, before the U-Boot timer driver starts.

> Look for
> 
>     clrsetbits_le32(RCB_REG(HPTC), 3, 1 << 7);
> 
> > +static int hpet_timer_get_count(struct udevice *dev, u64 *count)
> 
> > +static int hpet_timer_probe(struct udevice *dev)
> 
> > +#ifndef CONFIG_X86_TSC_TIMER
> 
> > +#define EARLY_HPET_BASE 0xfed00000
> 
> HPET address is fixed, AFAIU, on x86, and provided by config option in
> U-Boot.

Found it. Thank you!

> > +unsigned long notrace timer_early_get_rate(void)
> > +u64 notrace timer_early_get_count(void)
> > +int timer_init(void)
> These functions have too much code duplication with above.

I will move the duplicated code into static functions.