On Agilex7 and Stratix10 SoCs, secondary CPUs must be offlined before
a warm reboot to ensure a clean PSCI state. Register a reboot notifier
that calls remove_cpu() on each secondary CPU when SYS_RESTART is
triggered in REBOOT_WARM mode.

A snapshot of cpu_online_mask is taken before the loop since remove_cpu()
modifies the mask as CPUs go down. CPU 0 is excluded as it is typically
not hotpluggable. Failures are logged and the loop continues so the
reboot is not blocked by a single CPU that refuses to offline.
The of_device_id table carries a per-compatible pdata flag to enable the
notifier only on platforms that need it; Agilex5 leaves the flag unset.

The notifier is unregistered at the start of remove(), before async
channel teardown, to prevent a reboot notification from racing with
driver shutdown.

Signed-off-by: Adrian Ng Ho Yin <adrian.ho.yin.ng@altera.com>
---
changelog:
v1 -> v2:
- Drop workqueue fan-out: remove_cpu() serialises on device_hotplug_lock
  internally so concurrent workers provided no parallelism. Replace with
  a single sequential loop over a cpumask snapshot.
- Fix CPU identity bug: get_cpu()/put_cpu() did not prevent task migration
  and the notifier can run on any CPU before migrate_to_reboot_cpu().
  Exclude CPU 0 (typically not hotpluggable) and offline everything else.
- Fix pre-count race: the two-loop atomic pre-count had a window where a
  concurrent hotplug event could cause dec_and_test() to fire prematurely.
  Eliminated entirely along with the completion and timeout.
- Replace of_device_is_compatible() checks with a stratix10_svc_pdata
  struct carried in of_device_id.data, retrieved via of_device_get_match_data().
- Move psci_cpu_off_teardown() to the top of stratix10_svc_drv_remove(),
  before async channel teardown, to close the race where a warm-reboot
  notification could fire while the driver is being dismantled.
---
 drivers/firmware/stratix10-svc.c | 88 ++++++++++++++++++++++++++++++--
 1 file changed, 85 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/stratix10-svc.c b/drivers/firmware/stratix10-svc.c
index de938ab2db0b..e10550237ea1 100644
--- a/drivers/firmware/stratix10-svc.c
+++ b/drivers/firmware/stratix10-svc.c
@@ -24,6 +24,10 @@
 #include <linux/firmware/intel/stratix10-smc.h>
 #include <linux/firmware/intel/stratix10-svc-client.h>
 #include <linux/types.h>
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/of_device.h>
+#include <linux/reboot.h>
 
 /**
  * SVC_NUM_DATA_IN_FIFO - number of struct stratix10_svc_data in the FIFO
@@ -96,6 +100,14 @@
 #define STRATIX10_GET_SDM_STATUS_CODE(status) \
 	(FIELD_GET(STRATIX10_SDM_STATUS_MASK, status))
 
+struct stratix10_svc_pdata {
+	bool needs_psci_cpu_off;
+};
+
+static const struct stratix10_svc_pdata psci_cpu_off_pdata = {
+	.needs_psci_cpu_off = true,
+};
+
 typedef void (svc_invoke_fn)(unsigned long, unsigned long, unsigned long,
 			     unsigned long, unsigned long, unsigned long,
 			     unsigned long, unsigned long,
@@ -280,6 +292,7 @@ struct stratix10_svc_chan {
  * @svc: manages the list of client svc drivers
  * @sdm_lock: only allows a single command single response to SDM
  * @actrl: async control structure
+ * @psci_reboot_nb: reboot notifier for PSCI secondary CPU offlining
  * @chans: array of service channels
  *
  * This struct is used to create communication channels for service clients, to
@@ -296,6 +309,7 @@ struct stratix10_svc_controller {
 	struct stratix10_svc *svc;
 	struct mutex sdm_lock;
 	struct stratix10_async_ctrl actrl;
+	struct notifier_block psci_reboot_nb;
 	struct stratix10_svc_chan chans[] __counted_by(num_chans);
 };
 
@@ -1981,9 +1995,60 @@ void stratix10_svc_free_memory(struct stratix10_svc_chan *chan, void *kaddr)
 }
 EXPORT_SYMBOL_GPL(stratix10_svc_free_memory);
 
+static void psci_offline_secondary_cpus(struct stratix10_svc_controller *ctrl)
+{
+	cpumask_var_t mask;
+	int cpu, ret;
+
+	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
+		return;
+
+	/*
+	 * Snapshot cpu_online_mask before the loop; remove_cpu() modifies it
+	 * as each CPU is brought down. Always preserve CPU 0 (boot CPU) to
+	 * run the reboot.
+	 */
+	cpumask_copy(mask, cpu_online_mask);
+	cpumask_clear_cpu(0, mask);
+
+	/*
+	 * Offlining is best-effort: if a CPU refuses to go down we log the
+	 * error and continue so the remaining secondaries are still attempted
+	 * and the warm reboot can proceed.
+	 */
+	for_each_cpu(cpu, mask) {
+		ret = remove_cpu(cpu);
+		if (ret)
+			pr_err("psci_cpu_off: failed to offline CPU%d: %d\n",
+			       cpu, ret);
+	}
+
+	free_cpumask_var(mask);
+}
+
+static int psci_cpu_off_reboot_notifier(struct notifier_block *nb,
+					unsigned long action, void *data)
+{
+	struct stratix10_svc_controller *ctrl =
+		container_of(nb, struct stratix10_svc_controller, psci_reboot_nb);
+
+	if (reboot_mode != REBOOT_WARM)
+		return NOTIFY_DONE;
+
+	if (action == SYS_RESTART)
+		psci_offline_secondary_cpus(ctrl);
+
+	return NOTIFY_OK;
+}
+
+static void psci_cpu_off_teardown(struct stratix10_svc_controller *ctrl)
+{
+	unregister_reboot_notifier(&ctrl->psci_reboot_nb);
+}
+
 static const struct of_device_id stratix10_svc_drv_match[] = {
-	{.compatible = "intel,stratix10-svc"},
-	{.compatible = "intel,agilex-svc"},
+	{ .compatible = "intel,stratix10-svc", .data = &psci_cpu_off_pdata },
+	{ .compatible = "intel,agilex-svc",    .data = &psci_cpu_off_pdata },
 	{},
 };
 
@@ -2001,6 +2066,7 @@ static int stratix10_svc_drv_probe(struct platform_device *pdev)
 	struct gen_pool *genpool;
 	struct stratix10_svc_sh_memory *sh_memory;
 	struct stratix10_svc *svc = NULL;
+	const struct stratix10_svc_pdata *pdata = of_device_get_match_data(dev);
 
 	svc_invoke_fn *invoke_fn;
 	size_t fifo_size;
@@ -2040,13 +2106,25 @@ static int stratix10_svc_drv_probe(struct platform_device *pdev)
 	INIT_LIST_HEAD(&controller->node);
 	init_completion(&controller->complete_status);
 
+	if (pdata && pdata->needs_psci_cpu_off) {
+		controller->psci_reboot_nb.notifier_call =
+			psci_cpu_off_reboot_notifier;
+		controller->psci_reboot_nb.priority = INT_MAX;
+
+		ret = register_reboot_notifier(&controller->psci_reboot_nb);
+		if (ret) {
+			dev_err(dev, "failed to register reboot notifier: %d\n", ret);
+			goto err_destroy_pool;
+		}
+	}
+
 	ret = stratix10_svc_async_init(controller);
 	if (ret == -EOPNOTSUPP) {
 		dev_info(dev, "Intel Service Layer Driver Initialized (sync-only mode)\n");
 	} else if (ret) {
 		dev_dbg(dev, "Intel Service Layer Driver: Error on stratix10_svc_async_init %d\n",
 			ret);
-		goto err_destroy_pool;
+		goto err_free_notifier;
 	} else {
 		dev_info(dev, "Intel Service Layer Driver Initialized\n");
 	}
@@ -2110,6 +2188,8 @@ static int stratix10_svc_drv_probe(struct platform_device *pdev)
 	while (i--)
 		kfifo_free(&controller->chans[i].svc_fifo);
 	stratix10_svc_async_exit(controller);
+err_free_notifier:
+	psci_cpu_off_teardown(controller);
 err_destroy_pool:
 	gen_pool_destroy(genpool);
 
@@ -2122,6 +2202,8 @@ static void stratix10_svc_drv_remove(struct platform_device *pdev)
 	struct stratix10_svc_controller *ctrl = platform_get_drvdata(pdev);
 	struct stratix10_svc *svc = ctrl->svc;
 
+	psci_cpu_off_teardown(ctrl);
+
 	stratix10_svc_async_exit(ctrl);
 
 	of_platform_depopulate(ctrl->dev);
-- 
2.49.GIT