calibrate: Rework delay timer calibration

The header define in asm/timex,h and the naming of the function to read the
delay timer are confusing at best.

Convert it to a config switch selected by the archictures which provide the
functionality and rename the function to delay_read_timer(), which makes
the purpose clear. Move the declaration to linux/delay.h where it belongs.

Remove the resulting empty asm/timex.h files as well.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260410120317.978403520@kernel.org

arch/Kconfig

@@ -363,6 +363,9 @@ config ARCH_HAS_DMA_CLEAR_UNCACHED
 config ARCH_HAS_CPU_FINALIZE_INIT
 	bool
 
+config ARCH_HAS_DELAY_TIMER
+	bool
+
 # The architecture has a per-task state that includes the mm's PASID
 config ARCH_HAS_CPU_PASID
 	bool

arch/arm/Kconfig

@@ -11,6 +11,7 @@ config ARM
 	select ARCH_HAS_CPU_FINALIZE_INIT if MMU
 	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_HAS_DEBUG_VIRTUAL if MMU
+	select ARCH_HAS_DELAY_TIMER
 	select ARCH_HAS_DMA_ALLOC if MMU
 	select ARCH_HAS_DMA_OPS
 	select ARCH_HAS_DMA_WRITE_COMBINE if !ARM_DMA_MEM_BUFFERABLE

arch/arm/include/asm/delay.h

@@ -91,7 +91,6 @@ extern void __loop_udelay(unsigned long usecs);
 extern void __loop_const_udelay(unsigned long);
 
 /* Delay-loop timer registration. */
-#define ARCH_HAS_READ_CURRENT_TIMER
 extern void register_current_timer_delay(const struct delay_timer *timer);
 
 #endif /* __ASSEMBLY__ */

arch/arm/include/asm/timex.h

@@ -10,7 +10,10 @@
 #define _ASMARM_TIMEX_H
 
 typedef unsigned long cycles_t;
-#define get_cycles()	({ cycles_t c; read_current_timer(&c) ? 0 : c; })
+// Temporary workaround until timex.h is cleaned up
+bool delay_read_timer(unsigned long *t);
+
+#define get_cycles()	({ cycles_t c; delay_read_timer(&c) ? 0 : c; })
 #define random_get_entropy() (((unsigned long)get_cycles()) ?: random_get_entropy_fallback())
 
 #endif

arch/arm/lib/delay.c

@@ -12,7 +12,6 @@
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/timex.h>
 
 /*
  * Default to the loop-based delay implementation.
@@ -27,15 +26,14 @@ static const struct delay_timer *delay_timer;
 static bool delay_calibrated;
 static u64 delay_res;
 
-int read_current_timer(unsigned long *timer_val)
+bool delay_read_timer(unsigned long *timer_val)
 {
 	if (!delay_timer)
-		return -ENXIO;
-
+		return false;
 	*timer_val = delay_timer->read_current_timer();
-	return 0;
+	return true;
 }
-EXPORT_SYMBOL_GPL(read_current_timer);
+EXPORT_SYMBOL_GPL(delay_read_timer);
 
 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
 {

arch/hexagon/Kconfig

@@ -5,6 +5,7 @@ comment "Linux Kernel Configuration for Hexagon"
 config HEXAGON
 	def_bool y
 	select ARCH_32BIT_OFF_T
+	select ARCH_HAS_DELAY_TIMER
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select ARCH_NO_PREEMPT
 	select ARCH_WANT_FRAME_POINTERS

arch/hexagon/include/asm/timex.h

@@ -1,20 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
- */
-
-#ifndef _ASM_TIMEX_H
-#define _ASM_TIMEX_H
-
-#include <asm-generic/timex.h>
-#include <asm/hexagon_vm.h>
-
-#define ARCH_HAS_READ_CURRENT_TIMER
-
-static inline int read_current_timer(unsigned long *timer_val)
-{
-	*timer_val = __vmgettime();
-	return 0;
-}
-
-#endif

arch/hexagon/kernel/time.c

@@ -6,6 +6,7 @@
  */
 
 #include <linux/init.h>
+#include <linux/delay.h>
 #include <linux/clockchips.h>
 #include <linux/clocksource.h>
 #include <linux/interrupt.h>
@@ -17,7 +18,6 @@
 #include <linux/of_irq.h>
 #include <linux/module.h>
 
-#include <asm/delay.h>
 #include <asm/hexagon_vm.h>
 #include <asm/time.h>
 
@@ -231,3 +231,9 @@ void __udelay(unsigned long usecs)
 		cpu_relax(); /*  not sure how this improves readability  */
 }
 EXPORT_SYMBOL(__udelay);
+
+bool delay_read_timer(unsigned long *timer_val)
+{
+	*timer_val = __vmgettime();
+	return true;
+}

arch/openrisc/Kconfig

@@ -7,6 +7,7 @@
 config OPENRISC
 	def_bool y
 	select ARCH_32BIT_OFF_T
+	select ARCH_HAS_DELAY_TIMER
 	select ARCH_HAS_DMA_SET_UNCACHED
 	select ARCH_HAS_DMA_CLEAR_UNCACHED
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE

arch/openrisc/include/asm/timex.h

@@ -25,6 +25,4 @@ static inline cycles_t get_cycles(void)
 }
 #define get_cycles get_cycles
 
-#define ARCH_HAS_READ_CURRENT_TIMER
-
 #endif

arch/openrisc/lib/delay.c

@@ -13,18 +13,17 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/delay.h>
 #include <linux/export.h>
 #include <linux/init.h>
-#include <linux/timex.h>
+
 #include <asm/param.h>
-#include <asm/delay.h>
-#include <asm/timex.h>
 #include <asm/processor.h>
 
-int read_current_timer(unsigned long *timer_value)
+bool delay_read_timer(unsigned long *timer_value)
 {
 	*timer_value = get_cycles();
-	return 0;
+	return true;
 }
 
 void __delay(unsigned long cycles)

arch/riscv/Kconfig

@@ -29,6 +29,7 @@ config RISCV
 	select ARCH_HAS_DEBUG_VIRTUAL if MMU
 	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEBUG_WX
+	select ARCH_HAS_DELAY_TIMER
 	select ARCH_HAS_ELF_CORE_EFLAGS if BINFMT_ELF && ELF_CORE
 	select ARCH_HAS_FAST_MULTIPLIER
 	select ARCH_HAS_FORTIFY_SOURCE

arch/riscv/include/asm/timex.h

@@ -80,12 +80,4 @@ static inline u64 get_cycles64(void)
 	return ((u64)hi << 32) | lo;
 }
 #endif /* CONFIG_64BIT */
-
-#define ARCH_HAS_READ_CURRENT_TIMER
-static inline int read_current_timer(unsigned long *timer_val)
-{
-	*timer_val = get_cycles();
-	return 0;
-}
-
 #endif /* _ASM_RISCV_TIMEX_H */

arch/riscv/lib/delay.c

@@ -6,7 +6,6 @@
 #include <linux/delay.h>
 #include <linux/math.h>
 #include <linux/param.h>
-#include <linux/timex.h>
 #include <linux/types.h>
 #include <linux/export.h>
 
@@ -109,3 +108,9 @@ void ndelay(unsigned long nsecs)
 	__delay(ncycles >> NDELAY_SHIFT);
 }
 EXPORT_SYMBOL(ndelay);
+
+bool delay_read_timer(unsigned long *timer_val)
+{
+	*timer_val = get_cycles();
+	return true;
+}

arch/sparc/Kconfig

@@ -70,6 +70,7 @@ config SPARC32
 config SPARC64
 	def_bool 64BIT
 	select ALTERNATE_USER_ADDRESS_SPACE
+	select ARCH_HAS_DELAY_TIMER
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_KRETPROBES

arch/sparc/include/asm/timex_64.h

@@ -13,6 +13,4 @@
 typedef unsigned long cycles_t;
 #define get_cycles()	tick_ops->get_tick()
 
-#define ARCH_HAS_READ_CURRENT_TIMER
-
 #endif

arch/sparc/kernel/time_64.c

@@ -894,8 +894,8 @@ unsigned long long sched_clock(void)
 	return ((get_tick() * quotient) >> SPARC64_NSEC_PER_CYC_SHIFT) - offset;
 }
 
-int read_current_timer(unsigned long *timer_val)
+bool delay_read_timer(unsigned long *timer_val)
 {
 	*timer_val = get_tick();
-	return 0;
+	return true;
 }

arch/x86/Kconfig

@@ -80,6 +80,7 @@ config X86
 	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_HAS_DEBUG_VIRTUAL
 	select ARCH_HAS_DEBUG_VM_PGTABLE	if !X86_PAE
+	select ARCH_HAS_DELAY_TIMER
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_DMA_OPS			if GART_IOMMU || XEN
 	select ARCH_HAS_EARLY_DEBUG		if KGDB

arch/x86/include/asm/timex.h

@@ -13,6 +13,4 @@ static inline unsigned long random_get_entropy(void)
 }
 #define random_get_entropy random_get_entropy
 
-#define ARCH_HAS_READ_CURRENT_TIMER
-
 #endif /* _ASM_X86_TIMEX_H */

arch/x86/lib/delay.c

@@ -14,12 +14,10 @@
 
 #include <linux/export.h>
 #include <linux/sched.h>
-#include <linux/timex.h>
 #include <linux/preempt.h>
 #include <linux/delay.h>
 
 #include <asm/processor.h>
-#include <asm/delay.h>
 #include <asm/timer.h>
 #include <asm/mwait.h>
 
@@ -189,13 +187,13 @@ void use_mwaitx_delay(void)
 	delay_fn = delay_halt;
 }
 
-int read_current_timer(unsigned long *timer_val)
+bool delay_read_timer(unsigned long *timer_val)
 {
 	if (delay_fn == delay_tsc) {
 		*timer_val = rdtsc();
-		return 0;
+		return true;
 	}
-	return -1;
+	return false;
 }
 
 void __delay(unsigned long loops)

include/asm-generic/timex.h

@@ -13,11 +13,4 @@ static inline cycles_t get_cycles(void)
 }
 #endif
 
-/*
- * Architectures are encouraged to implement read_current_timer
- * and define this in order to avoid the expensive delay loop
- * calibration during boot.
- */
-#undef ARCH_HAS_READ_CURRENT_TIMER
-
 #endif /* __ASM_GENERIC_TIMEX_H */

include/linux/delay.h

@@ -17,6 +17,8 @@ extern unsigned long loops_per_jiffy;
 
 #include <asm/delay.h>
 
+bool delay_read_timer(unsigned long *t);
+
 /*
  * Using udelay() for intervals greater than a few milliseconds can
  * risk overflow for high loops_per_jiffy (high bogomips) machines. The

include/linux/timex.h

@@ -156,8 +156,6 @@ extern int do_clock_adjtime(const clockid_t which_clock, struct __kernel_timex *
 
 extern void hardpps(const struct timespec64 *, const struct timespec64 *);
 
-int read_current_timer(unsigned long *timer_val);
-
 /* The clock frequency of the i8253/i8254 PIT */
 #define PIT_TICK_RATE 1193182ul
 

init/calibrate.c

@@ -13,7 +13,6 @@
 #include <linux/printk.h>
 #include <linux/smp.h>
 #include <linux/stddef.h>
-#include <linux/timex.h>
 
 unsigned long lpj_fine;
 unsigned long preset_lpj;
@@ -25,9 +24,9 @@ static int __init lpj_setup(char *str)
 
 __setup("lpj=", lpj_setup);
 
-#ifdef ARCH_HAS_READ_CURRENT_TIMER
+#ifdef CONFIG_ARCH_HAS_DELAY_TIMER
 
-/* This routine uses the read_current_timer() routine and gets the
+/* This routine uses the delay_read_timer() routine and gets the
  * loops per jiffy directly, instead of guessing it using delay().
  * Also, this code tries to handle non-maskable asynchronous events
  * (like SMIs)
@@ -48,13 +47,13 @@ static unsigned long calibrate_delay_direct(void)
 	int min = -1;
 	int i;
 
-	if (read_current_timer(&pre_start) < 0 )
+	if (!delay_read_timer(&pre_start))
 		return 0;
 
 	/*
 	 * A simple loop like
 	 *	while ( jiffies < start_jiffies+1)
-	 *		start = read_current_timer();
+	 *		start = delay_read_timer();
 	 * will not do. As we don't really know whether jiffy switch
 	 * happened first or timer_value was read first. And some asynchronous
 	 * event can happen between these two events introducing errors in lpj.
@@ -72,22 +71,22 @@ static unsigned long calibrate_delay_direct(void)
 
 	for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
 		pre_start = 0;
-		read_current_timer(&start);
+		delay_read_timer(&start);
 		start_jiffies = jiffies;
 		while (time_before_eq(jiffies, start_jiffies + 1)) {
 			pre_start = start;
-			read_current_timer(&start);
+			delay_read_timer(&start);
 		}
-		read_current_timer(&post_start);
+		delay_read_timer(&post_start);
 
 		pre_end = 0;
 		end = post_start;
 		while (time_before_eq(jiffies, start_jiffies + 1 +
 					       DELAY_CALIBRATION_TICKS)) {
 			pre_end = end;
-			read_current_timer(&end);
+			delay_read_timer(&end);
 		}
-		read_current_timer(&post_end);
+		delay_read_timer(&post_end);
 
 		timer_rate_max = (post_end - pre_start) /
 					DELAY_CALIBRATION_TICKS;