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, 290 insertions, 0 deletions

diff --git a/drivers/video/fbdev/pmag-ba-fb.c b/drivers/video/fbdev/pmag-ba-fb.c
new file mode 100644
index 000000000..1e010520b
--- /dev/null
+++ b/drivers/video/fbdev/pmag-ba-fb.c
@@ -0,0 +1,290 @@
+/*
+ *	linux/drivers/video/pmag-ba-fb.c
+ *
+ *	PMAG-BA TURBOchannel Color Frame Buffer (CFB) card support,
+ *	derived from:
+ *	"HP300 Topcat framebuffer support (derived from macfb of all things)
+ *	Phil Blundell <philb@gnu.org> 1998", the original code can be
+ *	found in the file hpfb.c in the same directory.
+ *
+ *	Based on digital document:
+ * 	"PMAG-BA TURBOchannel Color Frame Buffer
+ *	 Functional Specification", Revision 1.2, August 27, 1990
+ *
+ *	DECstation related code Copyright (C) 1999, 2000, 2001 by
+ *	Michael Engel <engel@unix-ag.org>,
+ *	Karsten Merker <merker@linuxtag.org> and
+ *	Harald Koerfgen.
+ *	Copyright (c) 2005, 2006  Maciej W. Rozycki
+ *	Copyright (c) 2005  James Simmons
+ *
+ *	This file is subject to the terms and conditions of the GNU General
+ *	Public License.  See the file COPYING in the main directory of this
+ *	archive for more details.
+ */
+
+#include <linux/compiler.h>
+#include <linux/errno.h>
+#include <linux/fb.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/tc.h>
+#include <linux/types.h>
+
+#include <asm/io.h>
+
+#include <video/pmag-ba-fb.h>
+
+
+struct pmagbafb_par {
+	volatile void __iomem *mmio;
+	volatile u32 __iomem *dac;
+};
+
+
+static const struct fb_var_screeninfo pmagbafb_defined = {
+	.xres		= 1024,
+	.yres		= 864,
+	.xres_virtual	= 1024,
+	.yres_virtual	= 864,
+	.bits_per_pixel	= 8,
+	.red.length	= 8,
+	.green.length	= 8,
+	.blue.length	= 8,
+	.activate	= FB_ACTIVATE_NOW,
+	.height		= -1,
+	.width		= -1,
+	.accel_flags	= FB_ACCEL_NONE,
+	.pixclock	= 14452,
+	.left_margin	= 116,
+	.right_margin	= 12,
+	.upper_margin	= 34,
+	.lower_margin	= 0,
+	.hsync_len	= 128,
+	.vsync_len	= 3,
+	.sync		= FB_SYNC_ON_GREEN,
+	.vmode		= FB_VMODE_NONINTERLACED,
+};
+
+static const struct fb_fix_screeninfo pmagbafb_fix = {
+	.id		= "PMAG-BA",
+	.smem_len	= (1024 * 1024),
+	.type		= FB_TYPE_PACKED_PIXELS,
+	.visual		= FB_VISUAL_PSEUDOCOLOR,
+	.line_length	= 1024,
+	.mmio_len	= PMAG_BA_SIZE - PMAG_BA_BT459,
+};
+
+
+static inline void dac_write(struct pmagbafb_par *par, unsigned int reg, u8 v)
+{
+	writeb(v, par->dac + reg / 4);
+}
+
+static inline u8 dac_read(struct pmagbafb_par *par, unsigned int reg)
+{
+	return readb(par->dac + reg / 4);
+}
+
+
+/*
+ * Set the palette.
+ */
+static int pmagbafb_setcolreg(unsigned int regno, unsigned int red,
+			      unsigned int green, unsigned int blue,
+			      unsigned int transp, struct fb_info *info)
+{
+	struct pmagbafb_par *par = info->par;
+
+	if (regno >= info->cmap.len)
+		return 1;
+
+	red   >>= 8;	/* The cmap fields are 16 bits    */
+	green >>= 8;	/* wide, but the hardware colormap */
+	blue  >>= 8;	/* registers are only 8 bits wide */
+
+	mb();
+	dac_write(par, BT459_ADDR_LO, regno);
+	dac_write(par, BT459_ADDR_HI, 0x00);
+	wmb();
+	dac_write(par, BT459_CMAP, red);
+	wmb();
+	dac_write(par, BT459_CMAP, green);
+	wmb();
+	dac_write(par, BT459_CMAP, blue);
+
+	return 0;
+}
+
+static const struct fb_ops pmagbafb_ops = {
+	.owner		= THIS_MODULE,
+	FB_DEFAULT_IOMEM_OPS,
+	.fb_setcolreg	= pmagbafb_setcolreg,
+};
+
+
+/*
+ * Turn the hardware cursor off.
+ */
+static void pmagbafb_erase_cursor(struct fb_info *info)
+{
+	struct pmagbafb_par *par = info->par;
+
+	mb();
+	dac_write(par, BT459_ADDR_LO, 0x00);
+	dac_write(par, BT459_ADDR_HI, 0x03);
+	wmb();
+	dac_write(par, BT459_DATA, 0x00);
+}
+
+
+static int pmagbafb_probe(struct device *dev)
+{
+	struct tc_dev *tdev = to_tc_dev(dev);
+	resource_size_t start, len;
+	struct fb_info *info;
+	struct pmagbafb_par *par;
+	int err;
+
+	info = framebuffer_alloc(sizeof(struct pmagbafb_par), dev);
+	if (!info)
+		return -ENOMEM;
+
+	par = info->par;
+	dev_set_drvdata(dev, info);
+
+	if (fb_alloc_cmap(&info->cmap, 256, 0) < 0) {
+		printk(KERN_ERR "%s: Cannot allocate color map\n",
+		       dev_name(dev));
+		err = -ENOMEM;
+		goto err_alloc;
+	}
+
+	info->fbops = &pmagbafb_ops;
+	info->fix = pmagbafb_fix;
+	info->var = pmagbafb_defined;
+
+	/* Request the I/O MEM resource.  */
+	start = tdev->resource.start;
+	len = tdev->resource.end - start + 1;
+	if (!request_mem_region(start, len, dev_name(dev))) {
+		printk(KERN_ERR "%s: Cannot reserve FB region\n",
+		       dev_name(dev));
+		err = -EBUSY;
+		goto err_cmap;
+	}
+
+	/* MMIO mapping setup.  */
+	info->fix.mmio_start = start;
+	par->mmio = ioremap(info->fix.mmio_start, info->fix.mmio_len);
+	if (!par->mmio) {
+		printk(KERN_ERR "%s: Cannot map MMIO\n", dev_name(dev));
+		err = -ENOMEM;
+		goto err_resource;
+	}
+	par->dac = par->mmio + PMAG_BA_BT459;
+
+	/* Frame buffer mapping setup.  */
+	info->fix.smem_start = start + PMAG_BA_FBMEM;
+	info->screen_base = ioremap(info->fix.smem_start,
+					    info->fix.smem_len);
+	if (!info->screen_base) {
+		printk(KERN_ERR "%s: Cannot map FB\n", dev_name(dev));
+		err = -ENOMEM;
+		goto err_mmio_map;
+	}
+	info->screen_size = info->fix.smem_len;
+
+	pmagbafb_erase_cursor(info);
+
+	err = register_framebuffer(info);
+	if (err < 0) {
+		printk(KERN_ERR "%s: Cannot register framebuffer\n",
+		       dev_name(dev));
+		goto err_smem_map;
+	}
+
+	get_device(dev);
+
+	fb_info(info, "%s frame buffer device at %s\n",
+		info->fix.id, dev_name(dev));
+
+	return 0;
+
+
+err_smem_map:
+	iounmap(info->screen_base);
+
+err_mmio_map:
+	iounmap(par->mmio);
+
+err_resource:
+	release_mem_region(start, len);
+
+err_cmap:
+	fb_dealloc_cmap(&info->cmap);
+
+err_alloc:
+	framebuffer_release(info);
+	return err;
+}
+
+static int pmagbafb_remove(struct device *dev)
+{
+	struct tc_dev *tdev = to_tc_dev(dev);
+	struct fb_info *info = dev_get_drvdata(dev);
+	struct pmagbafb_par *par = info->par;
+	resource_size_t start, len;
+
+	put_device(dev);
+	unregister_framebuffer(info);
+	iounmap(info->screen_base);
+	iounmap(par->mmio);
+	start = tdev->resource.start;
+	len = tdev->resource.end - start + 1;
+	release_mem_region(start, len);
+	fb_dealloc_cmap(&info->cmap);
+	framebuffer_release(info);
+	return 0;
+}
+
+
+/*
+ * Initialize the framebuffer.
+ */
+static const struct tc_device_id pmagbafb_tc_table[] = {
+	{ "DEC     ", "PMAG-BA " },
+	{ }
+};
+MODULE_DEVICE_TABLE(tc, pmagbafb_tc_table);
+
+static struct tc_driver pmagbafb_driver = {
+	.id_table	= pmagbafb_tc_table,
+	.driver		= {
+		.name	= "pmagbafb",
+		.bus	= &tc_bus_type,
+		.probe	= pmagbafb_probe,
+		.remove	= pmagbafb_remove,
+	},
+};
+
+static int __init pmagbafb_init(void)
+{
+#ifndef MODULE
+	if (fb_get_options("pmagbafb", NULL))
+		return -ENXIO;
+#endif
+	return tc_register_driver(&pmagbafb_driver);
+}
+
+static void __exit pmagbafb_exit(void)
+{
+	tc_unregister_driver(&pmagbafb_driver);
+}
+
+
+module_init(pmagbafb_init);
+module_exit(pmagbafb_exit);
+
+MODULE_LICENSE("GPL");