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, 143 insertions, 0 deletions

diff --git a/drivers/video/fbdev/controlfb.h b/drivers/video/fbdev/controlfb.h
new file mode 100644
index 000000000..e779cca51
--- /dev/null
+++ b/drivers/video/fbdev/controlfb.h
@@ -0,0 +1,143 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * controlfb_hw.h: Constants of all sorts for controlfb
+ *
+ * Copyright (C) 1998 Daniel Jacobowitz <dan@debian.org>
+ *
+ * Based on an awful lot of code, including:
+ *
+ * control.c: Console support for PowerMac "control" display adaptor.
+ * Copyright (C) 1996 Paul Mackerras.
+ *
+ * The so far unpublished platinumfb.c
+ * Copyright (C) 1998 Jon Howell
+ */
+
+/*
+ * Structure of the registers for the RADACAL colormap device.
+ */
+struct cmap_regs {
+	unsigned char addr;	/* index for both cmap and misc registers */
+	char pad1[15];
+	unsigned char crsr;	/* cursor palette */
+	char pad2[15];
+	unsigned char dat;	/* RADACAL misc register data */
+	char pad3[15];
+	unsigned char lut;	/* cmap data */
+	char pad4[15];
+};
+
+/*
+ * Structure of the registers for the "control" display adaptor.
+ */
+#define PAD(x)	char x[12]
+
+struct preg {			/* padded register */
+	unsigned r;
+	char pad[12];
+};
+
+struct control_regs {
+	struct preg vcount;	/* vertical counter */
+	/* Vertical parameters are in units of 1/2 scan line */
+	struct preg vswin;	/* between vsblank and vssync */
+	struct preg vsblank;	/* vert start blank */
+	struct preg veblank;	/* vert end blank (display start) */
+	struct preg vewin;	/* between vesync and veblank */
+	struct preg vesync;	/* vert end sync */
+	struct preg vssync;	/* vert start sync */
+	struct preg vperiod;	/* vert period */
+	struct preg piped;	/* pipe delay hardware cursor */
+	/* Horizontal params are in units of 2 pixels */
+	struct preg hperiod;	/* horiz period - 2 */
+	struct preg hsblank;	/* horiz start blank */
+	struct preg heblank;	/* horiz end blank */
+	struct preg hesync;	/* horiz end sync */
+	struct preg hssync;	/* horiz start sync */
+	struct preg heq;	/* half horiz sync len */
+	struct preg hlfln;	/* half horiz period */
+	struct preg hserr;	/* horiz period - horiz sync len */
+	struct preg cnttst;
+	struct preg ctrl;	/* display control */
+	struct preg start_addr;	/* start address: 5 lsbs zero */
+	struct preg pitch;	/* addrs diff between scan lines */
+	struct preg mon_sense;	/* monitor sense bits */
+	struct preg vram_attr;	/* enable vram banks */
+	struct preg mode;
+	struct preg rfrcnt;	/* refresh count */
+	struct preg intr_ena;	/* interrupt enable */
+	struct preg intr_stat;	/* interrupt status */
+	struct preg res[5];
+};
+
+struct control_regints {
+	/* Vertical parameters are in units of 1/2 scan line */
+	unsigned vswin;	/* between vsblank and vssync */
+	unsigned vsblank;	/* vert start blank */
+	unsigned veblank;	/* vert end blank (display start) */
+	unsigned vewin;	/* between vesync and veblank */
+	unsigned vesync;	/* vert end sync */
+	unsigned vssync;	/* vert start sync */
+	unsigned vperiod;	/* vert period */
+	unsigned piped;		/* pipe delay hardware cursor */
+	/* Horizontal params are in units of 2 pixels */
+	/* Except, apparently, for hres > 1024 (or == 1280?) */
+	unsigned hperiod;	/* horiz period - 2 */
+	unsigned hsblank;	/* horiz start blank */
+	unsigned heblank;	/* horiz end blank */
+	unsigned hesync;	/* horiz end sync */
+	unsigned hssync;	/* horiz start sync */
+	unsigned heq;		/* half horiz sync len */
+	unsigned hlfln;		/* half horiz period */
+	unsigned hserr;		/* horiz period - horiz sync len */
+};
+	
+/*
+ * Dot clock rate is
+ * 3.9064MHz * 2**clock_params[2] * clock_params[1] / clock_params[0].
+ */
+struct control_regvals {
+	unsigned regs[16];		/* for vswin .. hserr */
+	unsigned char mode;
+	unsigned char radacal_ctrl;
+	unsigned char clock_params[3];
+};
+
+#define CTRLFB_OFF 16	/* position of pixel 0 in frame buffer */
+
+
+/*
+ * Best cmode supported by control
+ */
+struct max_cmodes {
+	int m[2];	/* 0: 2MB vram, 1: 4MB vram */
+};
+
+/*
+ * Video modes supported by macmodes.c
+ */
+static struct max_cmodes control_mac_modes[] = {
+	{{-1,-1}},	/* 512x384, 60Hz interlaced (NTSC) */
+	{{-1,-1}},	/* 512x384, 60Hz */
+	{{-1,-1}},	/* 640x480, 50Hz interlaced (PAL) */
+	{{-1,-1}},	/* 640x480, 60Hz interlaced (NTSC) */
+	{{ 2, 2}},	/* 640x480, 60Hz (VGA) */
+	{{ 2, 2}},	/* 640x480, 67Hz */
+	{{-1,-1}},	/* 640x870, 75Hz (portrait) */
+	{{-1,-1}},	/* 768x576, 50Hz (PAL full frame) */
+	{{ 2, 2}},	/* 800x600, 56Hz */
+	{{ 2, 2}},	/* 800x600, 60Hz */
+	{{ 2, 2}},	/* 800x600, 72Hz */
+	{{ 2, 2}},	/* 800x600, 75Hz */
+	{{ 1, 2}},	/* 832x624, 75Hz */
+	{{ 1, 2}},	/* 1024x768, 60Hz */
+	{{ 1, 2}},	/* 1024x768, 70Hz (or 72Hz?) */
+	{{ 1, 2}},	/* 1024x768, 75Hz (VESA) */
+	{{ 1, 2}},	/* 1024x768, 75Hz */
+	{{ 1, 2}},	/* 1152x870, 75Hz */
+	{{ 0, 1}},	/* 1280x960, 75Hz */
+	{{ 0, 1}},	/* 1280x1024, 75Hz */
+	{{ 1, 2}},	/* 1152x768, 60Hz */
+	{{ 0, 1}},	/* 1600x1024, 60Hz */
+};
+