s390/time: Convert MACHINE_HAS_SCC to machine_has_scc()

Use static branch(es) to implement and use machine_has_scc() instead
of a runtime check via MACHINE_HAS_SCC.

This comes with a cleanup of early time initialization: the initial
tod_clock_base value is now passed via the bootdata mechanism, instead
of using absolute lowcore as transport vehicle from the decompressor
to the kernel.

Also the early tod clock initialization is moved to the decompressor
which allows to use a static branch with machine_has_scc() within the
kernel.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

11 files changed, 38 insertions, 37 deletions

diff --git a/arch/s390/boot/head.S b/arch/s390/boot/head.S
index 0a47b16f6412..fe68c9253ea2 100644
--- a/arch/s390/boot/head.S
+++ b/arch/s390/boot/head.S
@@ -254,8 +254,9 @@ SYM_CODE_START_LOCAL(startup_normal)
 	xc	0xf00(256),0xf00
 	larl	%r13,.Lctl
 	lctlg	%c0,%c15,0(%r13)	# load control registers
-	stcke	__LC_BOOT_CLOCK
-	mvc	__LC_LAST_UPDATE_CLOCK(8),__LC_BOOT_CLOCK+1
+	larl	%r13,tod_clock_base
+	stcke	0(%r13)
+	mvc	__LC_LAST_UPDATE_CLOCK(8),1(%r13)
 	larl	%r13,6f
 	spt	0(%r13)
 	mvc	__LC_LAST_UPDATE_TIMER(8),0(%r13)
diff --git a/arch/s390/boot/printk.c b/arch/s390/boot/printk.c
index b4c66fa667d5..8cf6331bc060 100644
--- a/arch/s390/boot/printk.c
+++ b/arch/s390/boot/printk.c
@@ -8,6 +8,7 @@
 #include <asm/sections.h>
 #include <asm/lowcore.h>
 #include <asm/setup.h>
+#include <asm/timex.h>
 #include <asm/sclp.h>
 #include <asm/uv.h>
 #include "boot.h"
@@ -199,8 +200,7 @@ static void boot_console_earlyprintk(const char *buf)
 static char *add_timestamp(char *buf)
 {
 #ifdef CONFIG_PRINTK_TIME
-	union tod_clock *boot_clock = (union tod_clock *)&get_lowcore()->boot_clock;
-	unsigned long ns = tod_to_ns(get_tod_clock() - boot_clock->tod);
+	unsigned long ns = tod_to_ns(__get_tod_clock_monotonic());
 	char ts[MAX_NUMLEN];
 
 	*buf++ = '[';
diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index 8081f06ad258..1c7367a338cd 100644
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -10,6 +10,7 @@
 #include <asm/machine.h>
 #include <asm/cpu_mf.h>
 #include <asm/setup.h>
+#include <asm/timex.h>
 #include <asm/kasan.h>
 #include <asm/kexec.h>
 #include <asm/sclp.h>
@@ -35,6 +36,8 @@ unsigned long __bootdata_preserved(max_mappable);
 unsigned long __bootdata_preserved(page_noexec_mask);
 unsigned long __bootdata_preserved(segment_noexec_mask);
 unsigned long __bootdata_preserved(region_noexec_mask);
+union tod_clock __bootdata_preserved(tod_clock_base);
+u64 __bootdata_preserved(clock_comparator_max) = -1UL;
 
 u64 __bootdata_preserved(stfle_fac_list[16]);
 struct oldmem_data __bootdata_preserved(oldmem_data);
@@ -46,6 +49,20 @@ void error(char *x)
 	disabled_wait();
 }
 
+static void reset_tod_clock(void)
+{
+	union tod_clock clk;
+
+	if (store_tod_clock_ext_cc(&clk) == 0)
+		return;
+	/* TOD clock not running. Set the clock to Unix Epoch. */
+	if (set_tod_clock(TOD_UNIX_EPOCH) || store_tod_clock_ext_cc(&clk))
+		disabled_wait();
+	memset(&tod_clock_base, 0, sizeof(tod_clock_base));
+	tod_clock_base.tod = TOD_UNIX_EPOCH;
+	get_lowcore()->last_update_clock = TOD_UNIX_EPOCH;
+}
+
 static void detect_facilities(void)
 {
 	if (cpu_has_edat1())
@@ -60,6 +77,13 @@ static void detect_facilities(void)
 	}
 	if (IS_ENABLED(CONFIG_PCI) && test_facility(153))
 		set_machine_feature(MFEATURE_PCI_MIO);
+	reset_tod_clock();
+	if (test_facility(139) && (tod_clock_base.tod >> 63)) {
+		/* Enable signed clock comparator comparisons */
+		set_machine_feature(MFEATURE_SCC);
+		clock_comparator_max = -1UL >> 1;
+		local_ctl_set_bit(0, CR0_CLOCK_COMPARATOR_SIGN_BIT);
+	}
 }
 
 static int cmma_test_essa(void)
diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index 60c887cdbaec..8067edd120eb 100644
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -127,7 +127,7 @@ struct lowcore {
 	__u64	int_clock;			/* 0x0318 */
 	__u8	pad_0x0320[0x0328-0x0320];	/* 0x0320 */
 	__u64	clock_comparator;		/* 0x0328 */
-	__u64	boot_clock[2];			/* 0x0330 */
+	__u8	pad_0x0330[0x0340-0x0330];	/* 0x0330 */
 
 	/* Current process. */
 	__u64	current_task;			/* 0x0340 */
diff --git a/arch/s390/include/asm/machine.h b/arch/s390/include/asm/machine.h
index 488e5d641713..e0a0e4121d08 100644
--- a/arch/s390/include/asm/machine.h
+++ b/arch/s390/include/asm/machine.h
@@ -10,6 +10,7 @@
 
 #define MFEATURE_LOWCORE	0
 #define MFEATURE_PCI_MIO	1
+#define MFEATURE_SCC		2
 
 #ifndef __ASSEMBLY__
 
@@ -78,6 +79,7 @@ static __always_inline bool machine_has_##name(void)				\
 }
 
 DEFINE_MACHINE_HAS_FEATURE(relocated_lowcore, MFEATURE_LOWCORE)
+DEFINE_MACHINE_HAS_FEATURE(scc, MFEATURE_SCC)
 
 #endif /* __ASSEMBLY__ */
 #endif /* __ASM_S390_MACHINE_H */
diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h
index 5844f6e09162..b1f6ea1e000a 100644
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -24,7 +24,6 @@
 #define MACHINE_FLAG_ESOP	BIT(4)
 #define MACHINE_FLAG_TE		BIT(11)
 #define MACHINE_FLAG_TLB_GUEST	BIT(14)
-#define MACHINE_FLAG_SCC	BIT(17)
 
 #define LPP_MAGIC		BIT(31)
 #define LPP_PID_MASK		_AC(0xffffffff, UL)
@@ -76,7 +75,6 @@ extern unsigned long mio_wb_bit_mask;
 #define MACHINE_HAS_ESOP	(get_lowcore()->machine_flags & MACHINE_FLAG_ESOP)
 #define MACHINE_HAS_TE		(get_lowcore()->machine_flags & MACHINE_FLAG_TE)
 #define MACHINE_HAS_TLB_GUEST	(get_lowcore()->machine_flags & MACHINE_FLAG_TLB_GUEST)
-#define MACHINE_HAS_SCC		(get_lowcore()->machine_flags & MACHINE_FLAG_SCC)
 
 /*
  * Console mode. Override with conmode=
diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
index a9460bd6555b..bed8d0b5a282 100644
--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -13,6 +13,7 @@
 #include <linux/preempt.h>
 #include <linux/time64.h>
 #include <asm/lowcore.h>
+#include <asm/machine.h>
 #include <asm/asm.h>
 
 /* The value of the TOD clock for 1.1.1970. */
@@ -267,7 +268,7 @@ static __always_inline u128 eitod_to_ns(u128 todval)
  */
 static inline int tod_after(unsigned long a, unsigned long b)
 {
-	if (MACHINE_HAS_SCC)
+	if (machine_has_scc())
 		return (long) a > (long) b;
 	return a > b;
 }
@@ -281,7 +282,7 @@ static inline int tod_after(unsigned long a, unsigned long b)
  */
 static inline int tod_after_eq(unsigned long a, unsigned long b)
 {
-	if (MACHINE_HAS_SCC)
+	if (machine_has_scc())
 		return (long) a >= (long) b;
 	return a >= b;
 }
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index 36709112ae7a..1242e7435647 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -122,7 +122,6 @@ int main(void)
 	OFFSET(__LC_LAST_UPDATE_TIMER, lowcore, last_update_timer);
 	OFFSET(__LC_LAST_UPDATE_CLOCK, lowcore, last_update_clock);
 	OFFSET(__LC_INT_CLOCK, lowcore, int_clock);
-	OFFSET(__LC_BOOT_CLOCK, lowcore, boot_clock);
 	OFFSET(__LC_CURRENT, lowcore, current_task);
 	OFFSET(__LC_KERNEL_STACK, lowcore, kernel_stack);
 	OFFSET(__LC_ASYNC_STACK, lowcore, async_stack);
diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 9e673dab7c11..708f158cc60e 100644
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -64,21 +64,6 @@ static void __init kasan_early_init(void)
 #endif
 }
 
-static void __init reset_tod_clock(void)
-{
-	union tod_clock clk;
-
-	if (store_tod_clock_ext_cc(&clk) == 0)
-		return;
-	/* TOD clock not running. Set the clock to Unix Epoch. */
-	if (set_tod_clock(TOD_UNIX_EPOCH) || store_tod_clock_ext_cc(&clk))
-		disabled_wait();
-
-	memset(&tod_clock_base, 0, sizeof(tod_clock_base));
-	tod_clock_base.tod = TOD_UNIX_EPOCH;
-	get_lowcore()->last_update_clock = TOD_UNIX_EPOCH;
-}
-
 /*
  * Initialize storage key for kernel pages
  */
@@ -243,12 +228,6 @@ static __init void detect_machine_facilities(void)
 	}
 	if (test_facility(129))
 		system_ctl_set_bit(0, CR0_VECTOR_BIT);
-	if (test_facility(139) && (tod_clock_base.tod >> 63)) {
-		/* Enabled signed clock comparator comparisons */
-		get_lowcore()->machine_flags |= MACHINE_FLAG_SCC;
-		clock_comparator_max = -1ULL >> 1;
-		system_ctl_set_bit(0, CR0_CLOCK_COMPARATOR_SIGN_BIT);
-	}
 }
 
 static inline void save_vector_registers(void)
@@ -286,7 +265,6 @@ static void __init sort_amode31_extable(void)
 void __init startup_init(void)
 {
 	kasan_early_init();
-	reset_tod_clock();
 	time_early_init();
 	init_kernel_storage_key();
 	lockdep_off();
diff --git a/arch/s390/kernel/head64.S b/arch/s390/kernel/head64.S
index 396034b2fe67..7edb9ded199c 100644
--- a/arch/s390/kernel/head64.S
+++ b/arch/s390/kernel/head64.S
@@ -18,12 +18,10 @@
 
 __HEAD
 SYM_CODE_START(startup_continue)
-	larl	%r1,tod_clock_base
-	GET_LC	%r2
-	mvc	0(16,%r1),__LC_BOOT_CLOCK(%r2)
 #
 # Setup stack
 #
+	GET_LC	%r2
 	larl	%r14,init_task
 	stg	%r14,__LC_CURRENT(%r2)
 	larl	%r15,init_thread_union+STACK_INIT_OFFSET
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index e9f47c3a6197..ac58b1db40e6 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -54,10 +54,10 @@
 #include <asm/cio.h>
 #include "entry.h"
 
-union tod_clock tod_clock_base __section(".data");
+union tod_clock __bootdata_preserved(tod_clock_base);
 EXPORT_SYMBOL_GPL(tod_clock_base);
 
-u64 clock_comparator_max = -1ULL;
+u64 __bootdata_preserved(clock_comparator_max);
 EXPORT_SYMBOL_GPL(clock_comparator_max);
 
 static DEFINE_PER_CPU(struct clock_event_device, comparators);