x86: timer: use a timer base of 0

On x86 platforms the timer is reset to 0 when the SoC is reset. Having
this as the timer base is useful since it provides an indication of how
long it takes before U-Boot is running.

When U-Boot sets the timer base to something else, time is lost and we
no-longer have an accurate account of the time since reset. This
particularly affects bootstage.

Change the default to not read the timer base, leaving it at 0. Add an
option for when U-Boot is the secondary bootloader.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

diff --git a/arch/x86/cpu/coreboot/Kconfig b/arch/x86/cpu/coreboot/Kconfig
index 93f61f2..c8e6a88 100644 (file)
--- a/arch/x86/cpu/coreboot/Kconfig
+++ b/arch/x86/cpu/coreboot/Kconfig
@@ -24,5 +24,6 @@ config SYS_COREBOOT
        imply CMD_CBFS
        imply FS_CBFS
        imply CBMEM_CONSOLE
+       imply X86_TSC_READ_BASE
 
 endif

diff --git a/arch/x86/cpu/slimbootloader/Kconfig b/arch/x86/cpu/slimbootloader/Kconfig
index 3ea4c99..58a9ca0 100644 (file)
--- a/arch/x86/cpu/slimbootloader/Kconfig
+++ b/arch/x86/cpu/slimbootloader/Kconfig
@@ -17,3 +17,4 @@ config SYS_SLIMBOOTLOADER
        imply USB_EHCI_HCD
        imply USB_XHCI_HCD
        imply E1000
+       imply X86_TSC_READ_BASE

diff --git a/drivers/timer/Kconfig b/drivers/timer/Kconfig
index 5f4bc6e..41f9755 100644 (file)
--- a/drivers/timer/Kconfig
+++ b/drivers/timer/Kconfig
@@ -174,6 +174,20 @@ config X86_TSC_TIMER
        help
          Select this to enable Time-Stamp Counter (TSC) timer for x86.
 
+config X86_TSC_READ_BASE
+       bool "Read the TSC timer base on start-up"
+       depends on X86_TSC_TIMER
+       help
+         On x86 platforms the TSC timer tick starts at the value 0 on reset.
+         This it makes no sense to read the timer on boot and use that as the
+         base, since we will miss some time taken to load U-Boot, etc. This
+         delay is controlled by the SoC and we cannot reduce it, but for
+         bootstage we want to record the time since reset as accurately as
+         possible.
+
+         The only exception is when U-Boot is used as a secondary bootloader,
+         where this option should be enabled.
+
 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 0df551f..813817f 100644 (file)
--- a/drivers/timer/tsc_timer.c
+++ b/drivers/timer/tsc_timer.c
@@ -397,7 +397,8 @@ static void tsc_timer_ensure_setup(bool early)
 {
        if (gd->arch.tsc_inited)
                return;
-       gd->arch.tsc_base = rdtsc();
+       if (IS_ENABLED(CONFIG_X86_TSC_READ_BASE))
+               gd->arch.tsc_base = rdtsc();
 
        if (!gd->arch.clock_rate) {
                unsigned long fast_calibrate;

diff --git a/lib/efi/Kconfig b/lib/efi/Kconfig
index 919e314..93b8564 100644 (file)
--- a/lib/efi/Kconfig
+++ b/lib/efi/Kconfig
@@ -1,6 +1,7 @@
 config EFI
        bool "Support running U-Boot from EFI"
        depends on X86
+       imply X86_TSC_READ_BASE
        help
          U-Boot can be started from EFI on certain platforms. This allows
          EFI to perform most of the system init and then jump to U-Boot for