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, 54 insertions, 0 deletions

diff --git a/include/soc/microchip/mpfs.h b/include/soc/microchip/mpfs.h
new file mode 100644
index 000000000..ec04c98a8
--- /dev/null
+++ b/include/soc/microchip/mpfs.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *
+ * Microchip PolarFire SoC (MPFS)
+ *
+ * Copyright (c) 2020 Microchip Corporation. All rights reserved.
+ *
+ * Author: Conor Dooley <conor.dooley@microchip.com>
+ *
+ */
+
+#ifndef __SOC_MPFS_H__
+#define __SOC_MPFS_H__
+
+#include <linux/types.h>
+#include <linux/of_device.h>
+#include <linux/regmap.h>
+
+struct mpfs_sys_controller;
+
+struct mpfs_mss_msg {
+	u8 cmd_opcode;
+	u16 cmd_data_size;
+	struct mpfs_mss_response *response;
+	u8 *cmd_data;
+	u16 mbox_offset;
+	u16 resp_offset;
+};
+
+struct mpfs_mss_response {
+	u32 resp_status;
+	u32 *resp_msg;
+	u16 resp_size;
+};
+
+#if IS_ENABLED(CONFIG_POLARFIRE_SOC_SYS_CTRL)
+
+int mpfs_blocking_transaction(struct mpfs_sys_controller *mpfs_client, struct mpfs_mss_msg *msg);
+
+struct mpfs_sys_controller *mpfs_sys_controller_get(struct device *dev);
+
+struct mtd_info *mpfs_sys_controller_get_flash(struct mpfs_sys_controller *mpfs_client);
+
+#endif /* if IS_ENABLED(CONFIG_POLARFIRE_SOC_SYS_CTRL) */
+
+#if IS_ENABLED(CONFIG_MCHP_CLK_MPFS)
+#if IS_ENABLED(CONFIG_RESET_POLARFIRE_SOC)
+int mpfs_reset_controller_register(struct device *clk_dev, struct regmap *map);
+#else
+static inline int mpfs_reset_controller_register(struct device *clk_dev, void __iomem *base) { return 0; }
+#endif /* if IS_ENABLED(CONFIG_RESET_POLARFIRE_SOC) */
+#endif /* if IS_ENABLED(CONFIG_MCHP_CLK_MPFS) */
+
+#endif /* __SOC_MPFS_H__ */