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, 256 insertions, 0 deletions

diff --git a/drivers/reset/reset-intel-gw.c b/drivers/reset/reset-intel-gw.c
new file mode 100644
index 000000000..0db64cc8a
--- /dev/null
+++ b/drivers/reset/reset-intel-gw.c
@@ -0,0 +1,256 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2019 Intel Corporation.
+ * Lei Chuanhua <Chuanhua.lei@intel.com>
+ */
+
+#include <linux/bitfield.h>
+#include <linux/init.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/reboot.h>
+#include <linux/regmap.h>
+#include <linux/reset-controller.h>
+
+#define RCU_RST_STAT	0x0024
+#define RCU_RST_REQ	0x0048
+
+#define REG_OFFSET_MASK	GENMASK(31, 16)
+#define BIT_OFFSET_MASK	GENMASK(15, 8)
+#define STAT_BIT_OFFSET_MASK	GENMASK(7, 0)
+
+#define to_reset_data(x)	container_of(x, struct intel_reset_data, rcdev)
+
+struct intel_reset_soc {
+	bool legacy;
+	u32 reset_cell_count;
+};
+
+struct intel_reset_data {
+	struct reset_controller_dev rcdev;
+	const struct intel_reset_soc *soc_data;
+	struct regmap *regmap;
+	struct device *dev;
+	u32 reboot_id;
+};
+
+static const struct regmap_config intel_rcu_regmap_config = {
+	.name =		"intel-reset",
+	.reg_bits =	32,
+	.reg_stride =	4,
+	.val_bits =	32,
+};
+
+/*
+ * Reset status register offset relative to
+ * the reset control register(X) is X + 4
+ */
+static u32 id_to_reg_and_bit_offsets(struct intel_reset_data *data,
+				     unsigned long id, u32 *rst_req,
+				     u32 *req_bit, u32 *stat_bit)
+{
+	*rst_req = FIELD_GET(REG_OFFSET_MASK, id);
+	*req_bit = FIELD_GET(BIT_OFFSET_MASK, id);
+
+	if (data->soc_data->legacy)
+		*stat_bit = FIELD_GET(STAT_BIT_OFFSET_MASK, id);
+	else
+		*stat_bit = *req_bit;
+
+	if (data->soc_data->legacy && *rst_req == RCU_RST_REQ)
+		return RCU_RST_STAT;
+	else
+		return *rst_req + 0x4;
+}
+
+static int intel_set_clr_bits(struct intel_reset_data *data, unsigned long id,
+			      bool set)
+{
+	u32 rst_req, req_bit, rst_stat, stat_bit, val;
+	int ret;
+
+	rst_stat = id_to_reg_and_bit_offsets(data, id, &rst_req,
+					     &req_bit, &stat_bit);
+
+	val = set ? BIT(req_bit) : 0;
+	ret = regmap_update_bits(data->regmap, rst_req,  BIT(req_bit), val);
+	if (ret)
+		return ret;
+
+	return regmap_read_poll_timeout(data->regmap, rst_stat, val,
+					set == !!(val & BIT(stat_bit)), 20,
+					200);
+}
+
+static int intel_assert_device(struct reset_controller_dev *rcdev,
+			       unsigned long id)
+{
+	struct intel_reset_data *data = to_reset_data(rcdev);
+	int ret;
+
+	ret = intel_set_clr_bits(data, id, true);
+	if (ret)
+		dev_err(data->dev, "Reset assert failed %d\n", ret);
+
+	return ret;
+}
+
+static int intel_deassert_device(struct reset_controller_dev *rcdev,
+				 unsigned long id)
+{
+	struct intel_reset_data *data = to_reset_data(rcdev);
+	int ret;
+
+	ret = intel_set_clr_bits(data, id, false);
+	if (ret)
+		dev_err(data->dev, "Reset deassert failed %d\n", ret);
+
+	return ret;
+}
+
+static int intel_reset_status(struct reset_controller_dev *rcdev,
+			      unsigned long id)
+{
+	struct intel_reset_data *data = to_reset_data(rcdev);
+	u32 rst_req, req_bit, rst_stat, stat_bit, val;
+	int ret;
+
+	rst_stat = id_to_reg_and_bit_offsets(data, id, &rst_req,
+					     &req_bit, &stat_bit);
+	ret = regmap_read(data->regmap, rst_stat, &val);
+	if (ret)
+		return ret;
+
+	return !!(val & BIT(stat_bit));
+}
+
+static const struct reset_control_ops intel_reset_ops = {
+	.assert =	intel_assert_device,
+	.deassert =	intel_deassert_device,
+	.status	=	intel_reset_status,
+};
+
+static int intel_reset_xlate(struct reset_controller_dev *rcdev,
+			     const struct of_phandle_args *spec)
+{
+	struct intel_reset_data *data = to_reset_data(rcdev);
+	u32 id;
+
+	if (spec->args[1] > 31)
+		return -EINVAL;
+
+	id = FIELD_PREP(REG_OFFSET_MASK, spec->args[0]);
+	id |= FIELD_PREP(BIT_OFFSET_MASK, spec->args[1]);
+
+	if (data->soc_data->legacy) {
+		if (spec->args[2] > 31)
+			return -EINVAL;
+
+		id |= FIELD_PREP(STAT_BIT_OFFSET_MASK, spec->args[2]);
+	}
+
+	return id;
+}
+
+static int intel_reset_restart_handler(struct sys_off_data *data)
+{
+	struct intel_reset_data *reset_data = data->cb_data;
+
+	intel_assert_device(&reset_data->rcdev, reset_data->reboot_id);
+
+	return NOTIFY_DONE;
+}
+
+static int intel_reset_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct device *dev = &pdev->dev;
+	struct intel_reset_data *data;
+	void __iomem *base;
+	u32 rb_id[3];
+	int ret;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->soc_data = of_device_get_match_data(dev);
+	if (!data->soc_data)
+		return -ENODEV;
+
+	base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(base))
+		return PTR_ERR(base);
+
+	data->regmap = devm_regmap_init_mmio(dev, base,
+					     &intel_rcu_regmap_config);
+	if (IS_ERR(data->regmap)) {
+		dev_err(dev, "regmap initialization failed\n");
+		return PTR_ERR(data->regmap);
+	}
+
+	ret = device_property_read_u32_array(dev, "intel,global-reset", rb_id,
+					     data->soc_data->reset_cell_count);
+	if (ret) {
+		dev_err(dev, "Failed to get global reset offset!\n");
+		return ret;
+	}
+
+	data->dev =			dev;
+	data->rcdev.of_node =		np;
+	data->rcdev.owner =		dev->driver->owner;
+	data->rcdev.ops	=		&intel_reset_ops;
+	data->rcdev.of_xlate =		intel_reset_xlate;
+	data->rcdev.of_reset_n_cells =	data->soc_data->reset_cell_count;
+	ret = devm_reset_controller_register(&pdev->dev, &data->rcdev);
+	if (ret)
+		return ret;
+
+	data->reboot_id = FIELD_PREP(REG_OFFSET_MASK, rb_id[0]);
+	data->reboot_id |= FIELD_PREP(BIT_OFFSET_MASK, rb_id[1]);
+
+	if (data->soc_data->legacy)
+		data->reboot_id |= FIELD_PREP(STAT_BIT_OFFSET_MASK, rb_id[2]);
+
+	devm_register_restart_handler(&pdev->dev, intel_reset_restart_handler, data);
+
+	return 0;
+}
+
+static const struct intel_reset_soc xrx200_data = {
+	.legacy =		true,
+	.reset_cell_count =	3,
+};
+
+static const struct intel_reset_soc lgm_data = {
+	.legacy =		false,
+	.reset_cell_count =	2,
+};
+
+static const struct of_device_id intel_reset_match[] = {
+	{ .compatible = "intel,rcu-lgm", .data = &lgm_data },
+	{ .compatible = "intel,rcu-xrx200", .data = &xrx200_data },
+	{}
+};
+
+static struct platform_driver intel_reset_driver = {
+	.probe = intel_reset_probe,
+	.driver = {
+		.name = "intel-reset",
+		.of_match_table = intel_reset_match,
+	},
+};
+
+static int __init intel_reset_init(void)
+{
+	return platform_driver_register(&intel_reset_driver);
+}
+
+/*
+ * RCU is system core entity which is in Always On Domain whose clocks
+ * or resource initialization happens in system core initialization.
+ * Also, it is required for most of the platform or architecture
+ * specific devices to perform reset operation as part of initialization.
+ * So perform RCU as post core initialization.
+ */
+postcore_initcall(intel_reset_init);