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, 122 insertions, 0 deletions

diff --git a/drivers/reset/reset-raspberrypi.c b/drivers/reset/reset-raspberrypi.c
new file mode 100644
index 000000000..fa23db554
--- /dev/null
+++ b/drivers/reset/reset-raspberrypi.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Raspberry Pi 4 firmware reset driver
+ *
+ * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
+ */
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/reset-controller.h>
+#include <soc/bcm2835/raspberrypi-firmware.h>
+#include <dt-bindings/reset/raspberrypi,firmware-reset.h>
+
+struct rpi_reset {
+	struct reset_controller_dev rcdev;
+	struct rpi_firmware *fw;
+};
+
+static inline struct rpi_reset *to_rpi(struct reset_controller_dev *rcdev)
+{
+	return container_of(rcdev, struct rpi_reset, rcdev);
+}
+
+static int rpi_reset_reset(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	struct rpi_reset *priv = to_rpi(rcdev);
+	u32 dev_addr;
+	int ret;
+
+	switch (id) {
+	case RASPBERRYPI_FIRMWARE_RESET_ID_USB:
+		/*
+		 * The Raspberry Pi 4 gets its USB functionality from VL805, a
+		 * PCIe chip that implements xHCI. After a PCI reset, VL805's
+		 * firmware may either be loaded directly from an EEPROM or, if
+		 * not present, by the SoC's co-processor, VideoCore. rpi's
+		 * VideoCore OS contains both the non public firmware load
+		 * logic and the VL805 firmware blob. This triggers the
+		 * aforementioned process.
+		 *
+		 * The pci device address is expected is expected by the
+		 * firmware encoded like this:
+		 *
+		 *	PCI_BUS << 20 | PCI_SLOT << 15 | PCI_FUNC << 12
+		 *
+		 * But since rpi's PCIe is hardwired, we know the address in
+		 * advance.
+		 */
+		dev_addr = 0x100000;
+		ret = rpi_firmware_property(priv->fw, RPI_FIRMWARE_NOTIFY_XHCI_RESET,
+					    &dev_addr, sizeof(dev_addr));
+		if (ret)
+			return ret;
+
+		/* Wait for vl805 to startup */
+		usleep_range(200, 1000);
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static const struct reset_control_ops rpi_reset_ops = {
+	.reset	= rpi_reset_reset,
+};
+
+static int rpi_reset_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct rpi_firmware *fw;
+	struct device_node *np;
+	struct rpi_reset *priv;
+
+	np = of_get_parent(dev->of_node);
+	if (!np) {
+		dev_err(dev, "Missing firmware node\n");
+		return -ENOENT;
+	}
+
+	fw = devm_rpi_firmware_get(&pdev->dev, np);
+	of_node_put(np);
+	if (!fw)
+		return -EPROBE_DEFER;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	dev_set_drvdata(dev, priv);
+
+	priv->fw = fw;
+	priv->rcdev.owner = THIS_MODULE;
+	priv->rcdev.nr_resets = RASPBERRYPI_FIRMWARE_RESET_NUM_IDS;
+	priv->rcdev.ops = &rpi_reset_ops;
+	priv->rcdev.of_node = dev->of_node;
+
+	return devm_reset_controller_register(dev, &priv->rcdev);
+}
+
+static const struct of_device_id rpi_reset_of_match[] = {
+	{ .compatible = "raspberrypi,firmware-reset" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, rpi_reset_of_match);
+
+static struct platform_driver rpi_reset_driver = {
+	.probe	= rpi_reset_probe,
+	.driver	= {
+		.name = "raspberrypi-reset",
+		.of_match_table = rpi_reset_of_match,
+	},
+};
+module_platform_driver(rpi_reset_driver);
+
+MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@suse.de>");
+MODULE_DESCRIPTION("Raspberry Pi 4 firmware reset driver");
+MODULE_LICENSE("GPL");