arm/arm64: arch_timer: Use archdata to indicate vdso suitability

Instead of comparing the name to a magic string, use archdata to
explicitly communicate whether the arch timer is suitable for
direct vdso access.
Acked-by: NWill Deacon <will.deacon@arm.com>
Acked-by: NRussell King <rmk+kernel@armlinux.org.uk>
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NScott Wood <oss@buserror.net>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm/Kconfig

 config ARM
 	bool
 	default y
+	select ARCH_CLOCKSOURCE_DATA
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE

arch/arm/include/asm/clocksource.h

+#ifndef _ASM_CLOCKSOURCE_H
+#define _ASM_CLOCKSOURCE_H
+
+struct arch_clocksource_data {
+	bool vdso_direct;	/* Usable for direct VDSO access? */
+};
+
+#endif

arch/arm/kernel/vdso.c

@@ -270,7 +270,7 @@ static bool tk_is_cntvct(const struct timekeeper *tk)
 	if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
 		return false;
 
-	if (strcmp(tk->tkr_mono.clock->name, "arch_sys_counter") != 0)
+	if (!tk->tkr_mono.clock->archdata.vdso_direct)
 		return false;
 
 	return true;

arch/arm64/Kconfig

@@ -4,6 +4,7 @@ config ARM64
 	select ACPI_GENERIC_GSI if ACPI
 	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
 	select ACPI_MCFG if ACPI
+	select ARCH_CLOCKSOURCE_DATA
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE

arch/arm64/include/asm/clocksource.h

+#ifndef _ASM_CLOCKSOURCE_H
+#define _ASM_CLOCKSOURCE_H
+
+struct arch_clocksource_data {
+	bool vdso_direct;	/* Usable for direct VDSO access? */
+};
+
+#endif

arch/arm64/kernel/vdso.c

@@ -201,7 +201,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
  */
 void update_vsyscall(struct timekeeper *tk)
 {
-	u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter");
+	u32 use_syscall = !tk->tkr_mono.clock->archdata.vdso_direct;
 
 	++vdso_data->tb_seq_count;
 	smp_wmb();

drivers/clocksource/arm_arch_timer.c

@@ -602,23 +602,18 @@ static void __init arch_counter_register(unsigned type)
 		else
 			arch_timer_read_counter = arch_counter_get_cntpct;
 
+		clocksource_counter.archdata.vdso_direct = true;
+
 #ifdef CONFIG_FSL_ERRATUM_A008585
 		/*
 		 * Don't use the vdso fastpath if errata require using
 		 * the out-of-line counter accessor.
 		 */
 		if (static_branch_unlikely(&arch_timer_read_ool_enabled))
-			clocksource_counter.name = "arch_sys_counter_ool";
+			clocksource_counter.archdata.vdso_direct = false;
 #endif
 	} else {
 		arch_timer_read_counter = arch_counter_get_cntvct_mem;
-
-		/* If the clocksource name is "arch_sys_counter" the
-		 * VDSO will attempt to read the CP15-based counter.
-		 * Ensure this does not happen when CP15-based
-		 * counter is not available.
-		 */
-		clocksource_counter.name = "arch_mem_counter";
 	}
 
 	start_count = arch_timer_read_counter();