Hi Bin, On Fri, 11 Oct 2019 at 23:18, Bin Meng <bmeng...@gmail.com> wrote: > > Hi Simon, > > On Sat, Oct 12, 2019 at 11:38 AM Simon Glass <s...@chromium.org> wrote: > > > > Hi Bin, > > > > On Fri, 11 Oct 2019 at 07:19, Bin Meng <bmeng...@gmail.com> wrote: > > > > > > Hi Simon, > > > > > > On Fri, Oct 11, 2019 at 1:06 AM Simon Glass <s...@chromium.org> wrote: > > > > > > > > Hi Bin, > > > > > > > > On Sat, 5 Oct 2019 at 08:36, Bin Meng <bmeng...@gmail.com> wrote: > > > > > > > > > > Hi Simon, > > > > > > > > > > On Wed, Sep 25, 2019 at 10:58 PM Simon Glass <s...@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 <s...@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. > > > > > > Why? > > > > > > if (1) > > > panic("no timer"); > > > > > > then compiler does not generate any codes of the following? > > > > > > fast_calibrate = cpu_mhz_from_cpuid(); > > > > > > I don't understand. > > > > > > > The panic() function is marked as noreturn, so the compiler assume it > > doesn't return. You can try this if you like. It reduces the size by > > 700 bytes which on a 22KB image is a lot. > > OK, compiler is smart to generate less codes :) > > But the way you added the CONFIG_IS_ENABLED(..) logic check here is > obscure if one does not dig into that deep .. > > > > > > Besides, I think adding some random Kconfig options to exclude some > > > specific parts in one C file is a bad idea. It's unclear to me why we > > > should exclude one part versus another part. I'm OK to exclude the > > > whole C file for TPL/SPL though, but not part of it for size > > > limitation purpose. > > > > My understanding is the most of the code in this function is a > > fallback in case an earlier method doesn't work. But on modern CPUs > > Yes, correct. > > > the first method always works, so this is a waste of time? > > > > It's not a wast of time, but a bloat of the code size. As you said, > these are fallbacks, and methods are prioritized based on the age of > the processors, so that native method is tried first, followed by > cpuid, MSR, and finally PIT. > > You also mentioned that "on modern CPUs the first method always > works", so today the first method is native_calibrate_tsc(), but say 3 > years later, this might not be true, and chances are that we may add > another method before native_calibrate_tsc() for whatever mechanism is > used on the latest processors, and the insertion of the TPL Kconfig > option (TPL_X86_TSC_TIMER_NATIVE) check today is not future proof.
That's right, it is not. Perhaps we need to have separate timer drivers for different generations? But if not, I am loath to have 700 bytes of dead code in TPL, which I why I added the option. If we later need to adjust it, we can do so, but this cuts off the worst of the bloat. Regards, Simon _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot