From e2361e04b02aafa927c32c4f5a39e6fd96196082 Mon Sep 17 00:00:00 2001
From: "Bjoern A. Zeeb" <bz@FreeBSD.org>
Date: Mon, 31 Oct 2022 14:33:58 +0000
Subject: [PATCH] LinuxKPI: implement cpumask_of()

Add a static set of cpumasks for all (possible) cpus with only the one
indexed cpu enabled in each set.
This is needed for cpumask_of(_cpuid) which returns a cpumask (cpuset)
with only cpu _cpuid enabled and is used by one wireless driver at least.

MFC after:	3 days
Reviewed by:	emaste
Differential Revision: https://reviews.freebsd.org/D37223
---
 .../linuxkpi/common/include/linux/cpu.h       |  4 ++++
 sys/compat/linuxkpi/common/src/linux_compat.c | 20 +++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/sys/compat/linuxkpi/common/include/linux/cpu.h b/sys/compat/linuxkpi/common/include/linux/cpu.h
index 53fa9db424c2..08e59b33e53a 100644
--- a/sys/compat/linuxkpi/common/include/linux/cpu.h
+++ b/sys/compat/linuxkpi/common/include/linux/cpu.h
@@ -44,6 +44,8 @@ typedef	cpuset_t	cpumask_t;
 
 extern cpumask_t cpu_online_mask;
 
+cpumask_t *lkpi_get_static_single_cpu_mask(int);
+
 static __inline int
 cpumask_next(int cpuid, cpumask_t mask)
 {
@@ -73,4 +75,6 @@ cpumask_set_cpu(int cpu, cpumask_t *mask)
 	CPU_SET(cpu, mask);
 }
 
+#define	cpumask_of(_cpu)	(lkpi_get_static_single_cpu_mask(_cpu))
+
 #endif	/* _LINUXKPI_LINUX_CPU_H */
diff --git a/sys/compat/linuxkpi/common/src/linux_compat.c b/sys/compat/linuxkpi/common/src/linux_compat.c
index 8c5d2e4ecd16..1367556a6f43 100644
--- a/sys/compat/linuxkpi/common/src/linux_compat.c
+++ b/sys/compat/linuxkpi/common/src/linux_compat.c
@@ -132,6 +132,7 @@ static void linux_cdev_deref(struct linux_cdev *ldev);
 static struct vm_area_struct *linux_cdev_handle_find(void *handle);
 
 cpumask_t cpu_online_mask;
+static cpumask_t static_single_cpu_mask[MAXCPU];
 struct kobject linux_class_root;
 struct device linux_root_device;
 struct class linux_class_misc;
@@ -2734,6 +2735,16 @@ bool linux_cpu_has_clflush;
 struct cpuinfo_x86 boot_cpu_data;
 #endif
 
+cpumask_t *
+lkpi_get_static_single_cpu_mask(int cpuid)
+{
+
+	KASSERT((cpuid >= 0 && cpuid < MAXCPU), ("%s: invalid cpuid %d\n",
+	    __func__, cpuid));
+
+	return (&static_single_cpu_mask[cpuid]);
+}
+
 static void
 linux_compat_init(void *arg)
 {
@@ -2771,6 +2782,15 @@ linux_compat_init(void *arg)
 	init_waitqueue_head(&linux_var_waitq);
 
 	CPU_COPY(&all_cpus, &cpu_online_mask);
+	/*
+	 * Generate a single-CPU cpumask_t for each CPU (possibly) in the system.
+	 * CPUs are indexed from 0..(MAXCPU-1).  The entry for cpuid 0 will only
+	 * have itself in the cpumask, cupid 1 only itself on entry 1, and so on.
+	 * This is used by cpumask_of() (and possibly others in the future) for,
+	 * e.g., drivers to pass hints to irq_set_affinity_hint().
+	 */
+	for (i = 0; i < MAXCPU; i++)
+		CPU_SET(i, &static_single_cpu_mask[i]);
 }
 SYSINIT(linux_compat, SI_SUB_DRIVERS, SI_ORDER_SECOND, linux_compat_init, NULL);