[U-Boot] [PATCH 050/126] x86: timer: Reduce timer code size in TPL on Intel CPUs

[Simon Glass]

Hi Bin,

On Sat, 5 Oct 2019 at 08:36, Bin Meng <bmeng.cn at gmail.com> wrote:
>
> Hi Simon,
>
> On Wed, Sep 25, 2019 at 10:58 PM Simon Glass <sjg at chromium.org> wrote:
> >
> > Most of the timer-calibration methods are not needed on recent Intel CPUs
> > and just increase code size. Add an option to use the known-good way to
> > get the clock frequency in TPL. Size reduction is about 700 bytes.
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > ---
> >
> >  drivers/timer/Kconfig     | 29 +++++++++++++++++++----------
> >  drivers/timer/tsc_timer.c |  7 +++++--
> >  2 files changed, 24 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/timer/Kconfig b/drivers/timer/Kconfig
> > index 5f4bc6edb67..90bc8ec7c53 100644
> > --- a/drivers/timer/Kconfig
> > +++ b/drivers/timer/Kconfig
> > @@ -117,16 +117,6 @@ config RENESAS_OSTM_TIMER
> >           Enables support for the Renesas OSTM Timer driver.
> >           This timer is present on Renesas RZ/A1 R7S72100 SoCs.
> >
> > -config X86_TSC_TIMER_EARLY_FREQ
> > -       int "x86 TSC timer frequency in MHz when used as the early timer"
> > -       depends on X86_TSC_TIMER
> > -       default 1000
> > -       help
> > -         Sets the estimated CPU frequency in MHz when TSC is used as the
> > -         early timer and the frequency can neither be calibrated via some
> > -         hardware ways, nor got from device tree at the time when device
> > -         tree is not available yet.
> > -
> >  config OMAP_TIMER
> >         bool "Omap timer support"
> >         depends on TIMER
> > @@ -174,6 +164,25 @@ config X86_TSC_TIMER
> >         help
> >           Select this to enable Time-Stamp Counter (TSC) timer for x86.
> >
> > +config X86_TSC_TIMER_EARLY_FREQ
> > +       int "x86 TSC timer frequency in MHz when used as the early timer"
> > +       depends on X86_TSC_TIMER
> > +       default 1000
> > +       help
> > +         Sets the estimated CPU frequency in MHz when TSC is used as the
> > +         early timer and the frequency can neither be calibrated via some
> > +         hardware ways, nor got from device tree at the time when device
> > +         tree is not available yet.
> > +
> > +config TPL_X86_TSC_TIMER_NATIVE
> > +       bool "x86 TSC timer uses native calibration"
> > +       depends on TPL && X86_TSC_TIMER
> > +       help
> > +         Selects native timer calibration for TPL and don't include the other
> > +         methods in the code. This helps to reduce code size in TPL and works
> > +         on fairly modern Intel chips. Code-size reductions is about 700
> > +         bytes.
> > +
> >  config MTK_TIMER
> >         bool "MediaTek timer support"
> >         depends on TIMER
> > diff --git a/drivers/timer/tsc_timer.c b/drivers/timer/tsc_timer.c
> > index 919caba8a14..9630036bc7f 100644
> > --- a/drivers/timer/tsc_timer.c
> > +++ b/drivers/timer/tsc_timer.c
> > @@ -49,8 +49,7 @@ static unsigned long native_calibrate_tsc(void)
> >                 return 0;
> >
> >         crystal_freq = tsc_info.ecx / 1000;
> > -
> > -       if (!crystal_freq) {
> > +       if (!CONFIG_IS_ENABLED(X86_TSC_TIMER_NATIVE) && !crystal_freq) {
> >                 switch (gd->arch.x86_model) {
> >                 case INTEL_FAM6_SKYLAKE_MOBILE:
> >                 case INTEL_FAM6_SKYLAKE_DESKTOP:
> > @@ -405,6 +404,10 @@ static void tsc_timer_ensure_setup(bool early)
> >                 if (fast_calibrate)
> >                         goto done;
> >
> > +               /* Reduce code size by dropping other methods */
> > +               if (CONFIG_IS_ENABLED(X86_TSC_TIMER_NATIVE))
> > +                       panic("no timer");
> > +
>
> I don't get it. How could this reduce the code size? I don't see any
> #ifdefs around the other methods we want to drop?

The compiler sees that CONFIG_IS_ENABLED(..) is 1, and leaves out the
code that follows it.

>
> >                 fast_calibrate = cpu_mhz_from_cpuid();
> >                 if (fast_calibrate)
> >                         goto done;
> > --
>
> Regards,
> Bin

Regards,
Simon