[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>

4 files changed, 53 insertions, 115 deletions

diff --git a/src/include/ipxe/efi/efi_timer.h b/src/include/ipxe/efi/efi_timer.h
deleted file mode 100644
index c4987598..00000000
--- a/src/include/ipxe/efi/efi_timer.h
+++ /dev/null
@@ -1,36 +0,0 @@
-#ifndef _IPXE_EFI_TIMER_H
-#define _IPXE_EFI_TIMER_H
-
-/** @file
- *
- * iPXE timer API for EFI
- *
- */
-
-FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
-
-#ifdef TIMER_EFI
-#define TIMER_PREFIX_efi
-#else
-#define TIMER_PREFIX_efi __efi_
-#endif
-
-/**
- * Number of ticks per second
- *
- * This is a policy decision.
- */
-#define EFI_TICKS_PER_SEC 20
-
-/**
- * Get number of ticks per second
- *
- * @ret ticks_per_sec	Number of ticks per second
- */
-static inline __attribute__ (( always_inline )) unsigned long
-TIMER_INLINE ( efi, ticks_per_sec ) ( void ) {
-
-	return EFI_TICKS_PER_SEC;
-}
-
-#endif /* _IPXE_EFI_TIMER_H */
diff --git a/src/include/ipxe/linux/linux_timer.h b/src/include/ipxe/linux/linux_timer.h
deleted file mode 100644
index 7f46e36b..00000000
--- a/src/include/ipxe/linux/linux_timer.h
+++ /dev/null
@@ -1,18 +0,0 @@
-#ifndef _IPXE_LINUX_TIMER_H
-#define _IPXE_LINUX_TIMER_H
-
-/** @file
- *
- * iPXE timer API for Linux
- *
- */
-
-FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
-
-#ifdef TIMER_LINUX
-#define TIMER_PREFIX_linux
-#else
-#define TIMER_PREFIX_linux __linux_
-#endif
-
-#endif /* _IPXE_LINUX_TIMER_H */
diff --git a/src/include/ipxe/timer.h b/src/include/ipxe/timer.h
index 82fbb676..e6b95172 100644
--- a/src/include/ipxe/timer.h
+++ b/src/include/ipxe/timer.h
@@ -3,75 +3,77 @@
 
 /** @file
  *
- * iPXE timer API
+ * iPXE timers
  *
- * The timer API provides udelay() for fixed delays, and currticks()
- * for a monotonically increasing tick counter.
  */
 
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
-#include <ipxe/api.h>
-#include <config/timer.h>
+#include <ipxe/tables.h>
 
-/**
- * Calculate static inline timer API function name
- *
- * @v _prefix		Subsystem prefix
- * @v _api_func		API function
- * @ret _subsys_func	Subsystem API function
- */
-#define TIMER_INLINE( _subsys, _api_func ) \
-	SINGLE_API_INLINE ( TIMER_PREFIX_ ## _subsys, _api_func )
+/** Number of ticks per second */
+#define TICKS_PER_SEC 1024
 
-/**
- * Provide a timer API implementation
+/** Number of ticks per millisecond
  *
- * @v _prefix		Subsystem prefix
- * @v _api_func		API function
- * @v _func		Implementing function
+ * This is (obviously) not 100% consistent with the definition of
+ * TICKS_PER_SEC, but it allows for multiplications and divisions to
+ * be elided.  In any case, timer ticks are not expected to be a
+ * precision timing source; for example, the standard BIOS timer is
+ * based on an 18.2Hz clock.
  */
-#define PROVIDE_TIMER( _subsys, _api_func, _func ) \
-	PROVIDE_SINGLE_API ( TIMER_PREFIX_ ## _subsys, _api_func, _func )
+#define TICKS_PER_MS 1
 
-/**
- * Provide a static inline timer API implementation
- *
- * @v _prefix		Subsystem prefix
- * @v _api_func		API function
- */
-#define PROVIDE_TIMER_INLINE( _subsys, _api_func ) \
-	PROVIDE_SINGLE_API_INLINE ( TIMER_PREFIX_ ## _subsys, _api_func )
+/** A timer */
+struct timer {
+	/** Name */
+	const char *name;
+	/**
+	 * Probe timer
+	 *
+	 * @ret rc		Return status code
+	 */
+	int ( * probe ) ( void );
+	/**
+	 * Get current system time in ticks
+	 *
+	 * @ret ticks		Current time, in ticks
+	 */
+	unsigned long ( * currticks ) ( void );
+	/**
+	 * Delay for a fixed number of microseconds
+	 *
+	 * @v usecs		Number of microseconds for which to delay
+	 */
+	void ( * udelay ) ( unsigned long usecs );
+};
 
-/* Include all architecture-independent I/O API headers */
-#include <ipxe/efi/efi_timer.h>
-#include <ipxe/linux/linux_timer.h>
+/** Timer table */
+#define TIMERS __table ( struct timer, "timers" )
 
-/* Include all architecture-dependent I/O API headers */
-#include <bits/timer.h>
+/** Declare a timer */
+#define __timer( order ) __table_entry ( TIMERS, order )
 
-/**
- * Delay for a fixed number of microseconds
+/** @defgroup timer_order Timer detection order
  *
- * @v usecs		Number of microseconds for which to delay
+ * @{
  */
-void udelay ( unsigned long usecs );
 
-/**
- * Get current system time in ticks
- *
- * @ret ticks		Current time, in ticks
- */
-unsigned long currticks ( void );
+#define TIMER_PREFERRED	01	/**< Preferred timer */
+#define TIMER_NORMAL	02	/**< Normal timer */
 
-/**
- * Get number of ticks per second
+/** @} */
+
+/*
+ * sleep() prototype is defined by POSIX.1.  usleep() prototype is
+ * defined by 4.3BSD.  udelay() and mdelay() prototypes are chosen to
+ * be reasonably sensible.
  *
- * @ret ticks_per_sec	Number of ticks per second
  */
-unsigned long ticks_per_sec ( void );
 
-/** Number of ticks per second */
-#define TICKS_PER_SEC ( ticks_per_sec() )
+extern void udelay ( unsigned long usecs );
+extern void mdelay ( unsigned long msecs );
+extern unsigned long currticks ( void );
+extern unsigned int sleep ( unsigned int seconds );
 
 #endif /* _IPXE_TIMER_H */
diff --git a/src/include/unistd.h b/src/include/unistd.h
index d09e1ae3..6c31c060 100644
--- a/src/include/unistd.h
+++ b/src/include/unistd.h
@@ -23,19 +23,9 @@ extern int execv ( const char *command, char * const argv[] );
 		rc;							\
 	} )
 
-/* Pick up udelay() */
+/* Pick up udelay() and sleep() */
 #include <ipxe/timer.h>
 
-/*
- * sleep() prototype is defined by POSIX.1.  usleep() prototype is
- * defined by 4.3BSD.  udelay() and mdelay() prototypes are chosen to
- * be reasonably sensible.
- *
- */
-
-extern unsigned int sleep ( unsigned int seconds );
-extern void mdelay ( unsigned long msecs );
-
 static inline __always_inline void usleep ( unsigned long usecs ) {
 	udelay ( usecs );
 }