kernel: add platform_has() infrastructure

Add a simple infrastructure for setting, resetting and querying
platform feature flags.

Flags can be either global or architecture specific.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Tested-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> # Arm64 only
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Juergen Gross <jgross@suse.com>

MAINTAINERS

@@ -15824,6 +15824,14 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/iio/chemical/plantower,pms7003.yaml
 F:	drivers/iio/chemical/pms7003.c
 
+PLATFORM FEATURE INFRASTRUCTURE
+M:	Juergen Gross <jgross@suse.com>
+S:	Maintained
+F:	arch/*/include/asm/platform-feature.h
+F:	include/asm-generic/platform-feature.h
+F:	include/linux/platform-feature.h
+F:	kernel/platform-feature.c
+
 PLDMFW LIBRARY
 M:	Jacob Keller <jacob.e.keller@intel.com>
 S:	Maintained

include/asm-generic/Kbuild

@@ -44,6 +44,7 @@ mandatory-y += msi.h
 mandatory-y += pci.h
 mandatory-y += percpu.h
 mandatory-y += pgalloc.h
+mandatory-y += platform-feature.h
 mandatory-y += preempt.h
 mandatory-y += rwonce.h
 mandatory-y += sections.h

include/asm-generic/platform-feature.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_PLATFORM_FEATURE_H
+#define _ASM_GENERIC_PLATFORM_FEATURE_H
+
+/* Number of arch specific feature flags. */
+#define PLATFORM_ARCH_FEAT_N	0
+
+#endif /* _ASM_GENERIC_PLATFORM_FEATURE_H */

include/linux/platform-feature.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _PLATFORM_FEATURE_H
+#define _PLATFORM_FEATURE_H
+
+#include <linux/bitops.h>
+#include <asm/platform-feature.h>
+
+/* The platform features are starting with the architecture specific ones. */
+#define PLATFORM_FEAT_N				(0 + PLATFORM_ARCH_FEAT_N)
+
+void platform_set(unsigned int feature);
+void platform_clear(unsigned int feature);
+bool platform_has(unsigned int feature);
+
+#endif /* _PLATFORM_FEATURE_H */

kernel/Makefile

@@ -7,7 +7,7 @@ obj-y     = fork.o exec_domain.o panic.o \
 	    cpu.o exit.o softirq.o resource.o \
 	    sysctl.o capability.o ptrace.o user.o \
 	    signal.o sys.o umh.o workqueue.o pid.o task_work.o \
-	    extable.o params.o \
+	    extable.o params.o platform-feature.o \
 	    kthread.o sys_ni.o nsproxy.o \
 	    notifier.o ksysfs.o cred.o reboot.o \
 	    async.o range.o smpboot.o ucount.o regset.o

kernel/platform-feature.c

+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bitops.h>
+#include <linux/cache.h>
+#include <linux/export.h>
+#include <linux/platform-feature.h>
+
+#define PLATFORM_FEAT_ARRAY_SZ  BITS_TO_LONGS(PLATFORM_FEAT_N)
+static unsigned long __read_mostly platform_features[PLATFORM_FEAT_ARRAY_SZ];
+
+void platform_set(unsigned int feature)
+{
+	set_bit(feature, platform_features);
+}
+EXPORT_SYMBOL_GPL(platform_set);
+
+void platform_clear(unsigned int feature)
+{
+	clear_bit(feature, platform_features);
+}
+EXPORT_SYMBOL_GPL(platform_clear);
+
+bool platform_has(unsigned int feature)
+{
+	return test_bit(feature, platform_features);
+}
+EXPORT_SYMBOL_GPL(platform_has);