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

[Bin Meng]

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?

>                 fast_calibrate = cpu_mhz_from_cpuid();
>                 if (fast_calibrate)
>                         goto done;
> --

Regards,
Bin