PCI/pwrctl: Rescan bus on a separate thread

If we trigger the bus rescan from sysfs, we'll try to lock the PCI rescan
mutex recursively and deadlock - the platform device will be populated and
probed on the same thread that handles the sysfs write.

Add a workqueue to the pwrctl code on which we schedule the rescan for
controlled PCI devices. While at it: add a new interface for initializing
the pwrctl context where we'd now assign the parent device address and
initialize the workqueue.

Link: https://lore.kernel.org/r/20240823093323.33450-3-brgl@bgdev.pl
Fixes: 4565d265 ("PCI/pwrctl: Add PCI power control core code")
Reported-by: Konrad Dybcio <konradybcio@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/pci/pwrctl/core.c

@@ -48,6 +48,28 @@ static int pci_pwrctl_notify(struct notifier_block *nb, unsigned long action,
 	return NOTIFY_DONE;
 }
 
+static void rescan_work_func(struct work_struct *work)
+{
+	struct pci_pwrctl *pwrctl = container_of(work, struct pci_pwrctl, work);
+
+	pci_lock_rescan_remove();
+	pci_rescan_bus(to_pci_dev(pwrctl->dev->parent)->bus);
+	pci_unlock_rescan_remove();
+}
+
+/**
+ * pci_pwrctl_init() - Initialize the PCI power control context struct
+ *
+ * @pwrctl: PCI power control data
+ * @dev: Parent device
+ */
+void pci_pwrctl_init(struct pci_pwrctl *pwrctl, struct device *dev)
+{
+	pwrctl->dev = dev;
+	INIT_WORK(&pwrctl->work, rescan_work_func);
+}
+EXPORT_SYMBOL_GPL(pci_pwrctl_init);
+
 /**
  * pci_pwrctl_device_set_ready() - Notify the pwrctl subsystem that the PCI
  * device is powered-up and ready to be detected.
@@ -74,9 +96,7 @@ int pci_pwrctl_device_set_ready(struct pci_pwrctl *pwrctl)
 	if (ret)
 		return ret;
 
-	pci_lock_rescan_remove();
-	pci_rescan_bus(to_pci_dev(pwrctl->dev->parent)->bus);
-	pci_unlock_rescan_remove();
+	schedule_work(&pwrctl->work);
 
 	return 0;
 }

drivers/pci/pwrctl/pci-pwrctl-pwrseq.c

@@ -50,7 +50,7 @@ static int pci_pwrctl_pwrseq_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	data->ctx.dev = dev;
+	pci_pwrctl_init(&data->ctx, dev);
 
 	ret = devm_pci_pwrctl_device_set_ready(dev, &data->ctx);
 	if (ret)

include/linux/pci-pwrctl.h

@@ -7,6 +7,7 @@
 #define __PCI_PWRCTL_H__
 
 #include <linux/notifier.h>
+#include <linux/workqueue.h>
 
 struct device;
 struct device_link;
@@ -41,8 +42,10 @@ struct pci_pwrctl {
 	/* Private: don't use. */
 	struct notifier_block nb;
 	struct device_link *link;
+	struct work_struct work;
 };
 
+void pci_pwrctl_init(struct pci_pwrctl *pwrctl, struct device *dev);
 int pci_pwrctl_device_set_ready(struct pci_pwrctl *pwrctl);
 void pci_pwrctl_device_unset_ready(struct pci_pwrctl *pwrctl);
 int devm_pci_pwrctl_device_set_ready(struct device *dev,