x86/timer: Skip PIT initialization on modern chipsets

BugLink: https://bugs.launchpad.net/bugs/1851216
Recent Intel chipsets including Skylake and ApolloLake have a special
ITSSPRC register which allows the 8254 PIT to be gated.  When gated, the
8254 registers can still be programmed as normal, but there are no IRQ0
timer interrupts.

Some products such as the Connex L1430 and exone go Rugged E11 use this
register to ship with the PIT gated by default. This causes Linux to fail
to boot:

  Kernel panic - not syncing: IO-APIC + timer doesn't work! Boot with
  apic=debug and send a report.

The panic happens before the framebuffer is initialized, so to the user, it
appears as an early boot hang on a black screen.

Affected products typically have a BIOS option that can be used to enable
the 8254 and make Linux work (Chipset -> South Cluster Configuration ->
Miscellaneous Configuration -> 8254 Clock Gating), however it would be best
to make Linux support the no-8254 case.

Modern sytems allow to discover the TSC and local APIC timer frequencies,
so the calibration against the PIT is not required. These systems have
always running timers and the local APIC timer works also in deep power
states.

So the setup of the PIT including the IO-APIC timer interrupt delivery
checks are a pointless exercise.

Skip the PIT setup and the IO-APIC timer interrupt checks on these systems,
which avoids the panic caused by non ticking PITs and also speeds up the
boot process.

Thanks to Daniel for providing the changelog, initial analysis of the
problem and testing against a variety of machines.

Reported-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Daniel Drake <drake@endlessm.com>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: linux@endlessm.com
Cc: rafael.j.wysocki@intel.com
Cc: hdegoede@redhat.com
Link: https://lkml.kernel.org/r/20190628072307.24678-1-drake@endlessm.com
(backported from commit c8c4076723daca08bf35ccd68f22ea1c6219e207)
Signed-off-by: You-Sheng Yang <vicamo.yang@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 312d36b80afe148ff07f98801e3761a46fdbeb20..24a482cdb5b54b0ad7e1bc12cd9ecc1baa85d3aa 100644 (file)
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -175,6 +175,7 @@ extern void lapic_assign_system_vectors(void);
 extern void lapic_assign_legacy_vector(unsigned int isairq, bool replace);
 extern void lapic_online(void);
 extern void lapic_offline(void);
+extern bool apic_needs_pit(void);
 
 #else /* !CONFIG_X86_LOCAL_APIC */
 static inline void lapic_shutdown(void) { }
@@ -187,6 +188,7 @@ static inline void lapic_update_tsc_freq(void) { }
 static inline void apic_intr_mode_init(void) { }
 static inline void lapic_assign_system_vectors(void) { }
 static inline void lapic_assign_legacy_vector(unsigned int i, bool r) { }
+static inline bool apic_needs_pit(void) { return true; }
 #endif /* !CONFIG_X86_LOCAL_APIC */
 
 #ifdef CONFIG_X86_X2APIC

diff --git a/arch/x86/include/asm/time.h b/arch/x86/include/asm/time.h
index cef818b16045f6b1d8e511133081b72173d52d8b..8ac563abb567b3f4254beb5b35214cd83e30da3e 100644 (file)
--- a/arch/x86/include/asm/time.h
+++ b/arch/x86/include/asm/time.h
@@ -7,6 +7,7 @@
 
 extern void hpet_time_init(void);
 extern void time_init(void);
+extern bool pit_timer_init(void);
 
 extern struct clock_event_device *global_clock_event;
 

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index d8df5c9d6698a44e3bf0dd2dd0eb7a5f47558750..aff14a46b028d8b24cf5f12eb519ec6aa6e2b44d 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -796,6 +796,33 @@ calibrate_by_pmtimer(long deltapm, long *delta, long *deltatsc)
        return 0;
 }
 
+bool __init apic_needs_pit(void)
+{
+       /*
+        * If the frequencies are not known, PIT is required for both TSC
+        * and apic timer calibration.
+        */
+       if (!tsc_khz || !cpu_khz)
+               return true;
+
+       /* Is there an APIC at all? */
+       if (!boot_cpu_has(X86_FEATURE_APIC))
+               return true;
+
+       /* Deadline timer is based on TSC so no further PIT action required */
+       if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
+               return false;
+
+       /* APIC timer disabled? */
+       if (disable_apic_timer)
+               return true;
+       /*
+        * The APIC timer frequency is known already, no PIT calibration
+        * required. If unknown, let the PIT be initialized.
+        */
+       return lapic_timer_frequency == 0;
+}
+
 static int __init calibrate_APIC_clock(void)
 {
        struct clock_event_device *levt = this_cpu_ptr(&lapic_events);

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 3384e4bf59ffef0545699cb9bbe42997eb7f0c8f..2984715e8e5954d25874f8ece13d7d0c8c0bac37 100644 (file)
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -58,6 +58,7 @@
 #include <asm/acpi.h>
 #include <asm/dma.h>
 #include <asm/timer.h>
+#include <asm/time.h>
 #include <asm/i8259.h>
 #include <asm/setup.h>
 #include <asm/irq_remapping.h>
@@ -2135,6 +2136,9 @@ static inline void __init check_timer(void)
        unsigned long flags;
        int no_pin1 = 0;
 
+       if (!global_clock_event)
+               return;
+
        local_irq_save(flags);
 
        /*

diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c
index 0d307a657abbb253d4679471bd1ac202279ff447..2b7999a1a50a83b07084e93903786e15479684b8 100644 (file)
--- a/arch/x86/kernel/i8253.c
+++ b/arch/x86/kernel/i8253.c
@@ -8,6 +8,7 @@
 #include <linux/timex.h>
 #include <linux/i8253.h>
 
+#include <asm/apic.h>
 #include <asm/hpet.h>
 #include <asm/time.h>
 #include <asm/smp.h>
@@ -18,10 +19,32 @@
  */
 struct clock_event_device *global_clock_event;
 
-void __init setup_pit_timer(void)
+/*
+ * Modern chipsets can disable the PIT clock which makes it unusable. It
+ * would be possible to enable the clock but the registers are chipset
+ * specific and not discoverable. Avoid the whack a mole game.
+ *
+ * These platforms have discoverable TSC/CPU frequencies but this also
+ * requires to know the local APIC timer frequency as it normally is
+ * calibrated against the PIT interrupt.
+ */
+static bool __init use_pit(void)
+{
+       if (!IS_ENABLED(CONFIG_X86_TSC) || !boot_cpu_has(X86_FEATURE_TSC))
+               return true;
+
+       /* This also returns true when APIC is disabled */
+       return apic_needs_pit();
+}
+
+bool __init pit_timer_init(void)
 {
+       if (!use_pit())
+               return false;
+
        clockevent_i8253_init(true);
        global_clock_event = &i8253_clockevent;
+       return true;
 }
 
 #ifndef CONFIG_X86_64

diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
index f7e6bd4f48ad952770577643e4e605c2c5812599..5339ffd488d0239b9fad6f4780d15b27252f76d7 100644 (file)
--- a/arch/x86/kernel/time.c
+++ b/arch/x86/kernel/time.c
@@ -78,8 +78,11 @@ 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();
 }