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, 208 insertions, 0 deletions

diff --git a/drivers/video/fbdev/n411.c b/drivers/video/fbdev/n411.c
new file mode 100644
index 000000000..a36773133
--- /dev/null
+++ b/drivers/video/fbdev/n411.c
@@ -0,0 +1,208 @@
+/*
+ * linux/drivers/video/n411.c -- Platform device for N411 EPD kit
+ *
+ * Copyright (C) 2008, Jaya Kumar
+ *
+ * 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.
+ *
+ * Layout is based on skeletonfb.c by James Simmons and Geert Uytterhoeven.
+ *
+ * This driver is written to be used with the Hecuba display controller
+ * board, and tested with the EInk 800x600 display in 1 bit mode.
+ * The interface between Hecuba and the host is TTL based GPIO. The
+ * GPIO requirements are 8 writable data lines and 6 lines for control.
+ * Only 4 of the controls are actually used here but 6 for future use.
+ * The driver requires the IO addresses for data and control GPIO at
+ * load time. It is also possible to use this display with a standard
+ * PC parallel port.
+ *
+ * General notes:
+ * - User must set dio_addr=0xIOADDR cio_addr=0xIOADDR c2io_addr=0xIOADDR
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/fb.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/list.h>
+#include <linux/uaccess.h>
+#include <linux/irq.h>
+
+#include <video/hecubafb.h>
+
+static unsigned long dio_addr;
+static unsigned long cio_addr;
+static unsigned long c2io_addr;
+static unsigned long splashval;
+static unsigned int nosplash;
+static unsigned char ctl;
+
+static void n411_set_ctl(struct hecubafb_par *par, unsigned char bit, unsigned
+							char state)
+{
+	switch (bit) {
+	case HCB_CD_BIT:
+		if (state)
+			ctl &= ~(HCB_CD_BIT);
+		else
+			ctl |= HCB_CD_BIT;
+		break;
+	case HCB_DS_BIT:
+		if (state)
+			ctl &= ~(HCB_DS_BIT);
+		else
+			ctl |= HCB_DS_BIT;
+		break;
+	}
+	outb(ctl, cio_addr);
+}
+
+static unsigned char n411_get_ctl(struct hecubafb_par *par)
+{
+	return inb(c2io_addr);
+}
+
+static void n411_set_data(struct hecubafb_par *par, unsigned char value)
+{
+	outb(value, dio_addr);
+}
+
+static void n411_wait_for_ack(struct hecubafb_par *par, int clear)
+{
+	int timeout;
+	unsigned char tmp;
+
+	timeout = 500;
+	do {
+		tmp = n411_get_ctl(par);
+		if ((tmp & HCB_ACK_BIT) && (!clear))
+			return;
+		else if (!(tmp & HCB_ACK_BIT) && (clear))
+			return;
+		udelay(1);
+	} while (timeout--);
+	printk(KERN_ERR "timed out waiting for ack\n");
+}
+
+static int n411_init_control(struct hecubafb_par *par)
+{
+	unsigned char tmp;
+	/* for init, we want the following setup to be set:
+	WUP = lo
+	ACK = hi
+	DS = hi
+	RW = hi
+	CD = lo
+	*/
+
+	/* write WUP to lo, DS to hi, RW to hi, CD to lo */
+	ctl = HCB_WUP_BIT | HCB_RW_BIT | HCB_CD_BIT ;
+	n411_set_ctl(par, HCB_DS_BIT, 1);
+
+	/* check ACK is not lo */
+	tmp = n411_get_ctl(par);
+	if (tmp & HCB_ACK_BIT) {
+		printk(KERN_ERR "Fail because ACK is already low\n");
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
+
+static int n411_init_board(struct hecubafb_par *par)
+{
+	int retval;
+
+	retval = n411_init_control(par);
+	if (retval)
+		return retval;
+
+	par->send_command(par, APOLLO_INIT_DISPLAY);
+	par->send_data(par, 0x81);
+
+	/* have to wait while display resets */
+	udelay(1000);
+
+	/* if we were told to splash the screen, we just clear it */
+	if (!nosplash) {
+		par->send_command(par, APOLLO_ERASE_DISPLAY);
+		par->send_data(par, splashval);
+	}
+
+	return 0;
+}
+
+static struct hecuba_board n411_board = {
+	.owner			= THIS_MODULE,
+	.init			= n411_init_board,
+	.set_ctl		= n411_set_ctl,
+	.set_data		= n411_set_data,
+	.wait_for_ack		= n411_wait_for_ack,
+};
+
+static struct platform_device *n411_device;
+static int __init n411_init(void)
+{
+	int ret;
+	if (!dio_addr || !cio_addr || !c2io_addr) {
+		printk(KERN_WARNING "no IO addresses supplied\n");
+		return -EINVAL;
+	}
+
+	/* request our platform independent driver */
+	request_module("hecubafb");
+
+	n411_device = platform_device_alloc("hecubafb", -1);
+	if (!n411_device)
+		return -ENOMEM;
+
+	ret = platform_device_add_data(n411_device, &n411_board,
+				       sizeof(n411_board));
+	if (ret)
+		goto put_plat_device;
+
+	/* this _add binds hecubafb to n411. hecubafb refcounts n411 */
+	ret = platform_device_add(n411_device);
+
+	if (ret)
+		goto put_plat_device;
+
+	return 0;
+
+put_plat_device:
+	platform_device_put(n411_device);
+	return ret;
+}
+
+static void __exit n411_exit(void)
+{
+	platform_device_unregister(n411_device);
+}
+
+module_init(n411_init);
+module_exit(n411_exit);
+
+module_param(nosplash, uint, 0);
+MODULE_PARM_DESC(nosplash, "Disable doing the splash screen");
+module_param_hw(dio_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(dio_addr, "IO address for data, eg: 0x480");
+module_param_hw(cio_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(cio_addr, "IO address for control, eg: 0x400");
+module_param_hw(c2io_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(c2io_addr, "IO address for secondary control, eg: 0x408");
+module_param(splashval, ulong, 0);
+MODULE_PARM_DESC(splashval, "Splash pattern: 0x00 is black, 0x01 is white");
+
+MODULE_DESCRIPTION("board driver for n411 hecuba/apollo epd kit");
+MODULE_AUTHOR("Jaya Kumar");
+MODULE_LICENSE("GPL");
+