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, 56 insertions, 0 deletions

diff --git a/include/sound/sof/pm.h b/include/sound/sof/pm.h
new file mode 100644
index 000000000..df55bfe58
--- /dev/null
+++ b/include/sound/sof/pm.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause) */
+/*
+ * This file is provided under a dual BSD/GPLv2 license.  When using or
+ * redistributing this file, you may do so under either license.
+ *
+ * Copyright(c) 2018 Intel Corporation
+ */
+
+#ifndef __INCLUDE_SOUND_SOF_PM_H__
+#define __INCLUDE_SOUND_SOF_PM_H__
+
+#include <sound/sof/header.h>
+
+/*
+ * PM
+ */
+
+/* PM context element */
+struct sof_ipc_pm_ctx_elem {
+	struct sof_ipc_hdr hdr;
+	uint32_t type;
+	uint32_t size;
+	uint64_t addr;
+}  __packed;
+
+/*
+ * PM context - SOF_IPC_PM_CTX_SAVE, SOF_IPC_PM_CTX_RESTORE,
+ * SOF_IPC_PM_CTX_SIZE
+ */
+struct sof_ipc_pm_ctx {
+	struct sof_ipc_cmd_hdr hdr;
+	struct sof_ipc_host_buffer buffer;
+	uint32_t num_elems;
+	uint32_t size;
+
+	/* reserved for future use */
+	uint32_t reserved[8];
+
+	struct sof_ipc_pm_ctx_elem elems[];
+} __packed;
+
+/* enable or disable cores - SOF_IPC_PM_CORE_ENABLE */
+struct sof_ipc_pm_core_config {
+	struct sof_ipc_cmd_hdr hdr;
+	uint32_t enable_mask;
+} __packed;
+
+struct sof_ipc_pm_gate {
+	struct sof_ipc_cmd_hdr hdr;
+	uint32_t flags;	/* platform specific */
+
+	/* reserved for future use */
+	uint32_t reserved[5];
+} __packed;
+
+#endif