sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 98 insertions, 0 deletions

diff --git a/drivers/clk/versatile/clk-versatile.c b/drivers/clk/versatile/clk-versatile.c
new file mode 100644
index 000000000..8ed7a179f
--- /dev/null
+++ b/drivers/clk/versatile/clk-versatile.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Clock driver for the ARM Integrator/AP, Integrator/CP, Versatile AB and
+ * Versatile PB boards.
+ * Copyright (C) 2012 Linus Walleij
+ */
+#include <linux/clk-provider.h>
+#include <linux/err.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+
+#include "icst.h"
+#include "clk-icst.h"
+
+#define INTEGRATOR_HDR_LOCK_OFFSET	0x14
+
+#define VERSATILE_SYS_OSCCLCD_OFFSET	0x1c
+#define VERSATILE_SYS_LOCK_OFFSET	0x20
+
+/* Base offset for the core module */
+static void __iomem *cm_base;
+
+static const struct icst_params cp_auxosc_params = {
+	.vco_max	= ICST525_VCO_MAX_5V,
+	.vco_min	= ICST525_VCO_MIN,
+	.vd_min 	= 8,
+	.vd_max 	= 263,
+	.rd_min 	= 3,
+	.rd_max 	= 65,
+	.s2div		= icst525_s2div,
+	.idx2s		= icst525_idx2s,
+};
+
+static const struct clk_icst_desc cm_auxosc_desc __initconst = {
+	.params = &cp_auxosc_params,
+	.vco_offset = 0x1c,
+	.lock_offset = INTEGRATOR_HDR_LOCK_OFFSET,
+};
+
+static const struct icst_params versatile_auxosc_params = {
+	.vco_max	= ICST307_VCO_MAX,
+	.vco_min	= ICST307_VCO_MIN,
+	.vd_min		= 4 + 8,
+	.vd_max		= 511 + 8,
+	.rd_min		= 1 + 2,
+	.rd_max		= 127 + 2,
+	.s2div		= icst307_s2div,
+	.idx2s		= icst307_idx2s,
+};
+
+static const struct clk_icst_desc versatile_auxosc_desc __initconst = {
+	.params = &versatile_auxosc_params,
+	.vco_offset = VERSATILE_SYS_OSCCLCD_OFFSET,
+	.lock_offset = VERSATILE_SYS_LOCK_OFFSET,
+};
+static void __init cm_osc_setup(struct device_node *np,
+				const struct clk_icst_desc *desc)
+{
+	struct clk *clk;
+	const char *clk_name = np->name;
+	const char *parent_name;
+
+	if (!cm_base) {
+		/* Remap the core module base if not done yet */
+		struct device_node *parent;
+
+		parent = of_get_parent(np);
+		if (!parent) {
+			pr_err("no parent on core module clock\n");
+			return;
+		}
+		cm_base = of_iomap(parent, 0);
+		of_node_put(parent);
+		if (!cm_base) {
+			pr_err("could not remap core module base\n");
+			return;
+		}
+	}
+
+	parent_name = of_clk_get_parent_name(np, 0);
+	clk = icst_clk_register(NULL, desc, clk_name, parent_name, cm_base);
+	if (!IS_ERR(clk))
+		of_clk_add_provider(np, of_clk_src_simple_get, clk);
+}
+
+static void __init of_integrator_cm_osc_setup(struct device_node *np)
+{
+	cm_osc_setup(np, &cm_auxosc_desc);
+}
+CLK_OF_DECLARE(integrator_cm_auxosc_clk,
+	"arm,integrator-cm-auxosc", of_integrator_cm_osc_setup);
+
+static void __init of_versatile_cm_osc_setup(struct device_node *np)
+{
+	cm_osc_setup(np, &versatile_auxosc_desc);
+}
+CLK_OF_DECLARE(versatile_cm_auxosc_clk,
+	       "arm,versatile-cm-auxosc", of_versatile_cm_osc_setup);