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, 74 insertions, 0 deletions

diff --git a/include/dt-bindings/clock/pxa-clock.h b/include/dt-bindings/clock/pxa-clock.h
new file mode 100644
index 000000000..ce3d6b6a2
--- /dev/null
+++ b/include/dt-bindings/clock/pxa-clock.h
@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Inspired by original work from pxa2xx-regs.h by Nicolas Pitre
+ * Copyright (C) 2014 Robert Jarzmik
+ */
+
+#ifndef __DT_BINDINGS_CLOCK_PXA2XX_H__
+#define __DT_BINDINGS_CLOCK_PXA2XX_H__
+
+#define CLK_NONE 0
+#define CLK_1WIRE 1
+#define CLK_AC97 2
+#define CLK_AC97CONF 3
+#define CLK_ASSP 4
+#define CLK_BOOT 5
+#define CLK_BTUART 6
+#define CLK_CAMERA 7
+#define CLK_CIR 8
+#define CLK_CORE 9
+#define CLK_DMC 10
+#define CLK_FFUART 11
+#define CLK_FICP 12
+#define CLK_GPIO 13
+#define CLK_HSIO2 14
+#define CLK_HWUART 15
+#define CLK_I2C 16
+#define CLK_I2S 17
+#define CLK_IM 18
+#define CLK_INC 19
+#define CLK_ISC 20
+#define CLK_KEYPAD 21
+#define CLK_LCD 22
+#define CLK_MEMC 23
+#define CLK_MEMSTK 24
+#define CLK_MINI_IM 25
+#define CLK_MINI_LCD 26
+#define CLK_MMC 27
+#define CLK_MMC1 28
+#define CLK_MMC2 29
+#define CLK_MMC3 30
+#define CLK_MSL 31
+#define CLK_MSL0 32
+#define CLK_MVED 33
+#define CLK_NAND 34
+#define CLK_NSSP 35
+#define CLK_OSTIMER 36
+#define CLK_PWM0 37
+#define CLK_PWM1 38
+#define CLK_PWM2 39
+#define CLK_PWM3 40
+#define CLK_PWRI2C 41
+#define CLK_PXA300_GCU 42
+#define CLK_PXA320_GCU 43
+#define CLK_SMC 44
+#define CLK_SSP 45
+#define CLK_SSP1 46
+#define CLK_SSP2 47
+#define CLK_SSP3 48
+#define CLK_SSP4 49
+#define CLK_STUART 50
+#define CLK_TOUCH 51
+#define CLK_TPM 52
+#define CLK_UDC 53
+#define CLK_USB 54
+#define CLK_USB2 55
+#define CLK_USBH 56
+#define CLK_USBHOST 57
+#define CLK_USIM 58
+#define CLK_USIM1 59
+#define CLK_USMI0 60
+#define CLK_OSC32k768 61
+#define CLK_MAX 62
+
+#endif