[time] Allow timer to be selected at runtime

Allow the active timer (providing udelay() and currticks()) to be
selected at runtime based on probing during the INIT_EARLY stage of
initialisation.

TICKS_PER_SEC is now a fixed compile-time constant for all builds, and
is independent of the underlying clock tick rate.  We choose the value
1024 to allow multiplications and divisions on seconds to be converted
to bit shifts.

TICKS_PER_MS is defined as 1, allowing multiplications and divisions
on milliseconds to be omitted entirely.  The 2% inaccuracy in this
definition is negligible when using the standard BIOS timer (running
at around 18.2Hz).

TIMER_RDTSC now checks for a constant TSC before claiming to be a
usable timer.  (This timer can be tested in KVM via the command-line
option "-cpu host,+invtsc".)

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 16 insertions, 6 deletions

diff --git a/src/interface/efi/efi_timer.c b/src/interface/efi/efi_timer.c
index 1fd9971e..0ffe2a1a 100644
--- a/src/interface/efi/efi_timer.c
+++ b/src/interface/efi/efi_timer.c
@@ -36,6 +36,13 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  *
  */
 
+/**
+ * Number of jiffies per second
+ *
+ * This is a policy decision.
+ */
+#define EFI_JIFFIES_PER_SEC 32
+
 /** Current tick count */
 static unsigned long efi_jiffies;
 
@@ -95,7 +102,7 @@ static unsigned long efi_currticks ( void ) {
 	if ( efi_shutdown_in_progress )
 		efi_jiffies++;
 
-	return efi_jiffies;
+	return ( efi_jiffies * ( TICKS_PER_SEC / EFI_JIFFIES_PER_SEC ) );
 }
 
 /**
@@ -133,7 +140,7 @@ static void efi_tick_startup ( void ) {
 
 	/* Start timer tick */
 	if ( ( efirc = bs->SetTimer ( efi_tick_event, TimerPeriodic,
-				      ( 10000000 / EFI_TICKS_PER_SEC ) ) ) !=0){
+				      ( 10000000 / EFI_JIFFIES_PER_SEC ) ))!=0){
 		rc = -EEFI ( efirc );
 		DBGC ( colour, "EFI could not start timer tick: %s\n",
 		       strerror ( rc ) );
@@ -141,7 +148,7 @@ static void efi_tick_startup ( void ) {
 		return;
 	}
 	DBGC ( colour, "EFI timer started at %d ticks per second\n",
-	       EFI_TICKS_PER_SEC );
+	       EFI_JIFFIES_PER_SEC );
 }
 
 /**
@@ -180,6 +187,9 @@ struct startup_fn efi_tick_startup_fn __startup_fn ( STARTUP_EARLY ) = {
 	.shutdown = efi_tick_shutdown,
 };
 
-PROVIDE_TIMER ( efi, udelay, efi_udelay );
-PROVIDE_TIMER ( efi, currticks, efi_currticks );
-PROVIDE_TIMER_INLINE ( efi, ticks_per_sec );
+/** EFI timer */
+struct timer efi_timer __timer ( TIMER_NORMAL ) = {
+	.name = "efi",
+	.currticks = efi_currticks,
+	.udelay = efi_udelay,
+};