[coreboot-gerrit] Change in coreboot[master]: soc/intel/common: Select USE_LEGACY_8254_TIMER

[Michael Niewöhner (Code Review)]

Michael Niewöhner has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/34709 )

Change subject: soc/intel/common: Select USE_LEGACY_8254_TIMER
......................................................................

Patch Set 2: Code-Review-1

(3 comments)

https://review.coreboot.org/c/coreboot/+/34709/2//COMMIT_MSG 
Commit Message:

https://review.coreboot.org/c/coreboot/+/34709/2//COMMIT_MSG@17 
PS2, Line 17: * SeaBios
this is not true anymore for years. seabios can use 8254 (pit), pm timer and even tsc.

https://review.coreboot.org/c/coreboot/+/34709/2//COMMIT_MSG@20 
PS2, Line 20: * Linux <5.3
hmm, as I read that patch, that problem only occurs, when both hpet and pit is not available.

diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
index 0e14f6c0d35e0..07c0e960b3f3b 100644
--- a/arch/x86/kernel/time.c
+++ b/arch/x86/kernel/time.c
@@ -82,8 +82,11 @@ static void __init setup_default_timer_irq(void)
 /* Default timer init function */
 void __init hpet_time_init(void)
 {
-	if (!hpet_enable())
-		setup_pit_timer();
+	if (!hpet_enable()) {
+		if (!pit_timer_init())
+			return;
+	}
+
    setup_default_timer_irq();
 }

https://review.coreboot.org/c/coreboot/+/34709/2//COMMIT_MSG@26 
PS2, Line 26: GRUB2
GRUB2 supports other timers, too, but obviously not when booting from SeaBIOS. That seems to be a problem that IMO should be solved upstream in GRUB2 by trying other timers (pm, tsc) in legacy mode, too, instead of adding a workaround in coreboot.

grub-core/kern/i386/tsc.c

```
#if defined (GRUB_MACHINE_XEN) || defined (GRUB_MACHINE_XEN_PVH)
  (void) (grub_tsc_calibrate_from_xen () || calibrate_tsc_hardcode());
#elif defined (GRUB_MACHINE_EFI)
  (void) (grub_tsc_calibrate_from_pmtimer () || grub_tsc_calibrate_from_pit () || grub_tsc_calibrate_from_efi() || calibrate_tsc_hardcode());
#elif defined (GRUB_MACHINE_COREBOOT)
  (void) (grub_tsc_calibrate_from_pmtimer () || grub_tsc_calibrate_from_pit () || calibrate_tsc_hardcode());
#else
  (void) (grub_tsc_calibrate_from_pit () || calibrate_tsc_hardcode());
```