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, 204 insertions, 0 deletions

diff --git a/drivers/input/tablet/kbtab.c b/drivers/input/tablet/kbtab.c
new file mode 100644
index 000000000..6ce70c8e2
--- /dev/null
+++ b/drivers/input/tablet/kbtab.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb/input.h>
+#include <linux/unaligned.h>
+
+/*
+ * Pressure-threshold modules param code from Alex Perry <alex.perry@ieee.org>
+ */
+
+MODULE_AUTHOR("Josh Myer <josh@joshisanerd.com>");
+MODULE_DESCRIPTION("USB KB Gear JamStudio Tablet driver");
+MODULE_LICENSE("GPL");
+
+#define USB_VENDOR_ID_KBGEAR	0x084e
+
+static int kb_pressure_click = 0x10;
+module_param(kb_pressure_click, int, 0);
+MODULE_PARM_DESC(kb_pressure_click, "pressure threshold for clicks");
+
+struct kbtab {
+	unsigned char *data;
+	dma_addr_t data_dma;
+	struct input_dev *dev;
+	struct usb_interface *intf;
+	struct urb *irq;
+	char phys[32];
+};
+
+static void kbtab_irq(struct urb *urb)
+{
+	struct kbtab *kbtab = urb->context;
+	unsigned char *data = kbtab->data;
+	struct input_dev *dev = kbtab->dev;
+	int pressure;
+	int retval;
+
+	switch (urb->status) {
+	case 0:
+		/* success */
+		break;
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* this urb is terminated, clean up */
+		dev_dbg(&kbtab->intf->dev,
+			"%s - urb shutting down with status: %d\n",
+			__func__, urb->status);
+		return;
+	default:
+		dev_dbg(&kbtab->intf->dev,
+			"%s - nonzero urb status received: %d\n",
+			__func__, urb->status);
+		goto exit;
+	}
+
+
+	input_report_key(dev, BTN_TOOL_PEN, 1);
+
+	input_report_abs(dev, ABS_X, get_unaligned_le16(&data[1]));
+	input_report_abs(dev, ABS_Y, get_unaligned_le16(&data[3]));
+
+	/*input_report_key(dev, BTN_TOUCH , data[0] & 0x01);*/
+	input_report_key(dev, BTN_RIGHT, data[0] & 0x02);
+
+	pressure = data[5];
+	if (kb_pressure_click == -1)
+		input_report_abs(dev, ABS_PRESSURE, pressure);
+	else
+		input_report_key(dev, BTN_LEFT, pressure > kb_pressure_click ? 1 : 0);
+
+	input_sync(dev);
+
+ exit:
+	retval = usb_submit_urb(urb, GFP_ATOMIC);
+	if (retval)
+		dev_err(&kbtab->intf->dev,
+			"%s - usb_submit_urb failed with result %d\n",
+			__func__, retval);
+}
+
+static const struct usb_device_id kbtab_ids[] = {
+	{ USB_DEVICE(USB_VENDOR_ID_KBGEAR, 0x1001), .driver_info = 0 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(usb, kbtab_ids);
+
+static int kbtab_open(struct input_dev *dev)
+{
+	struct kbtab *kbtab = input_get_drvdata(dev);
+	struct usb_device *udev = interface_to_usbdev(kbtab->intf);
+
+	kbtab->irq->dev = udev;
+	if (usb_submit_urb(kbtab->irq, GFP_KERNEL))
+		return -EIO;
+
+	return 0;
+}
+
+static void kbtab_close(struct input_dev *dev)
+{
+	struct kbtab *kbtab = input_get_drvdata(dev);
+
+	usb_kill_urb(kbtab->irq);
+}
+
+static int kbtab_probe(struct usb_interface *intf, const struct usb_device_id *id)
+{
+	struct usb_device *dev = interface_to_usbdev(intf);
+	struct usb_endpoint_descriptor *endpoint;
+	struct kbtab *kbtab;
+	struct input_dev *input_dev;
+	int error = -ENOMEM;
+
+	if (intf->cur_altsetting->desc.bNumEndpoints < 1)
+		return -ENODEV;
+
+	endpoint = &intf->cur_altsetting->endpoint[0].desc;
+	if (!usb_endpoint_is_int_in(endpoint))
+		return -ENODEV;
+
+	kbtab = kzalloc_obj(*kbtab);
+	input_dev = input_allocate_device();
+	if (!kbtab || !input_dev)
+		goto fail1;
+
+	kbtab->data = usb_alloc_coherent(dev, 8, GFP_KERNEL, &kbtab->data_dma);
+	if (!kbtab->data)
+		goto fail1;
+
+	kbtab->irq = usb_alloc_urb(0, GFP_KERNEL);
+	if (!kbtab->irq)
+		goto fail2;
+
+	kbtab->intf = intf;
+	kbtab->dev = input_dev;
+
+	usb_make_path(dev, kbtab->phys, sizeof(kbtab->phys));
+	strlcat(kbtab->phys, "/input0", sizeof(kbtab->phys));
+
+	input_dev->name = "KB Gear Tablet";
+	input_dev->phys = kbtab->phys;
+	usb_to_input_id(dev, &input_dev->id);
+	input_dev->dev.parent = &intf->dev;
+
+	input_set_drvdata(input_dev, kbtab);
+
+	input_dev->open = kbtab_open;
+	input_dev->close = kbtab_close;
+
+	input_dev->evbit[0] |= BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_LEFT)] |=
+		BIT_MASK(BTN_LEFT) | BIT_MASK(BTN_RIGHT);
+	input_dev->keybit[BIT_WORD(BTN_DIGI)] |=
+		BIT_MASK(BTN_TOOL_PEN) | BIT_MASK(BTN_TOUCH);
+	input_set_abs_params(input_dev, ABS_X, 0, 0x2000, 4, 0);
+	input_set_abs_params(input_dev, ABS_Y, 0, 0x1750, 4, 0);
+	input_set_abs_params(input_dev, ABS_PRESSURE, 0, 0xff, 0, 0);
+
+	usb_fill_int_urb(kbtab->irq, dev,
+			 usb_rcvintpipe(dev, endpoint->bEndpointAddress),
+			 kbtab->data, 8,
+			 kbtab_irq, kbtab, endpoint->bInterval);
+	kbtab->irq->transfer_dma = kbtab->data_dma;
+	kbtab->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+
+	error = input_register_device(kbtab->dev);
+	if (error)
+		goto fail3;
+
+	usb_set_intfdata(intf, kbtab);
+
+	return 0;
+
+ fail3:	usb_free_urb(kbtab->irq);
+ fail2:	usb_free_coherent(dev, 8, kbtab->data, kbtab->data_dma);
+ fail1:	input_free_device(input_dev);
+	kfree(kbtab);
+	return error;
+}
+
+static void kbtab_disconnect(struct usb_interface *intf)
+{
+	struct kbtab *kbtab = usb_get_intfdata(intf);
+	struct usb_device *udev = interface_to_usbdev(intf);
+
+	usb_set_intfdata(intf, NULL);
+
+	input_unregister_device(kbtab->dev);
+	usb_free_urb(kbtab->irq);
+	usb_free_coherent(udev, 8, kbtab->data, kbtab->data_dma);
+	kfree(kbtab);
+}
+
+static struct usb_driver kbtab_driver = {
+	.name =		"kbtab",
+	.probe =	kbtab_probe,
+	.disconnect =	kbtab_disconnect,
+	.id_table =	kbtab_ids,
+};
+
+module_usb_driver(kbtab_driver);