s390/pci: implement reset_slot for hotplug slot

This is done by adding a zpci_hot_reset_device() call which does a low
level reset of the PCI function without changing its higher level
function state. This way it can be used while the zPCI function is bound
to a driver and with DMA tables being controlled either through the
IOMMU or DMA APIs which is prohibited when using zpci_disable_device()
as that drop existing DMA translations.

As this reset, unlike a normal FLR, also calls zpci_clear_irq() we need
to implement arch_restore_msi_irqs() and make sure we re-enable IRQs for
the PCI function if they were previously disabled.

Reviewed-by: Pierre Morel <[e-mail]>
Reviewed-by: Matthew Rosato <[e-mail]>
Signed-off-by: Niklas Schnelle <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>

arch/s390/include/asm/pci.h

···
 void zpci_device_reserved(struct zpci_dev *zdev);
 bool zpci_is_device_configured(struct zpci_dev *zdev);
 
+int zpci_hot_reset_device(struct zpci_dev *zdev);
 int zpci_register_ioat(struct zpci_dev *, u8, u64, u64, u64);
 int zpci_unregister_ioat(struct zpci_dev *, u8);
 void zpci_remove_reserved_devices(void);

arch/s390/pci/pci.c

···
 }
 
 /**
+ * zpci_hot_reset_device - perform a reset of the given zPCI function
+ * @zdev: the slot which should be reset
+ *
+ * Performs a low level reset of the zPCI function. The reset is low level in
+ * the sense that the zPCI function can be reset without detaching it from the
+ * common PCI subsystem. The reset may be performed while under control of
+ * either DMA or IOMMU APIs in which case the existing DMA/IOMMU translation
+ * table is reinstated at the end of the reset.
+ *
+ * After the reset the functions internal state is reset to an initial state
+ * equivalent to its state during boot when first probing a driver.
+ * Consequently after reset the PCI function requires re-initialization via the
+ * common PCI code including re-enabling IRQs via pci_alloc_irq_vectors()
+ * and enabling the function via e.g.pci_enablde_device_flags().The caller
+ * must guard against concurrent reset attempts.
+ *
+ * In most cases this function should not be called directly but through
+ * pci_reset_function() or pci_reset_bus() which handle the save/restore and
+ * locking.
+ *
+ * Return: 0 on success and an error value otherwise
+ */
+int zpci_hot_reset_device(struct zpci_dev *zdev)
+{
+	int rc;
+
+	zpci_dbg(3, "rst fid:%x, fh:%x\n", zdev->fid, zdev->fh);
+	if (zdev_enabled(zdev)) {
+		/* Disables device access, DMAs and IRQs (reset state) */
+		rc = zpci_disable_device(zdev);
+		/*
+		 * Due to a z/VM vs LPAR inconsistency in the error state the
+		 * FH may indicate an enabled device but disable says the
+		 * device is already disabled don't treat it as an error here.
+		 */
+		if (rc == -EINVAL)
+			rc = 0;
+		if (rc)
+			return rc;
+	}
+
+	rc = zpci_enable_device(zdev);
+	if (rc)
+		return rc;
+
+	if (zdev->dma_table)
+		rc = zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
+					(u64)zdev->dma_table);
+	else
+		rc = zpci_dma_init_device(zdev);
+	if (rc) {
+		zpci_disable_device(zdev);
+		return rc;
+	}
+
+	return 0;
+}
+
+/**
  * zpci_create_device() - Create a new zpci_dev and add it to the zbus
  * @fid: Function ID of the device to be created
  * @fh: Current Function Handle of the device to be created

arch/s390/pci/pci_irq.c

···
 		airq_iv_free(zpci_ibv[0], zdev->msi_first_bit, zdev->msi_nr_irqs);
 }
 
+void arch_restore_msi_irqs(struct pci_dev *pdev)
+{
+	struct zpci_dev *zdev = to_zpci(pdev);
+
+	if (!zdev->irqs_registered)
+		zpci_set_irq(zdev);
+	default_restore_msi_irqs(pdev);
+}
+
 static struct airq_struct zpci_airq = {
 	.handler = zpci_floating_irq_handler,
 	.isc = PCI_ISC,

drivers/pci/hotplug/s390_pci_hpc.c

···
 	return zpci_deconfigure_device(zdev);
 }
 
+static int reset_slot(struct hotplug_slot *hotplug_slot, bool probe)
+{
+	struct zpci_dev *zdev = container_of(hotplug_slot, struct zpci_dev,
+					     hotplug_slot);
+
+	if (zdev->state != ZPCI_FN_STATE_CONFIGURED)
+		return -EIO;
+	/*
+	 * We can't take the zdev->lock as reset_slot may be called during
+	 * probing and/or device removal which already happens under the
+	 * zdev->lock. Instead the user should use the higher level
+	 * pci_reset_function() or pci_bus_reset() which hold the PCI device
+	 * lock preventing concurrent removal. If not using these functions
+	 * holding the PCI device lock is required.
+	 */
+
+	/* As long as the function is configured we can reset */
+	if (probe)
+		return 0;
+
+	return zpci_hot_reset_device(zdev);
+}
+
 static int get_power_status(struct hotplug_slot *hotplug_slot, u8 *value)
 {
 	struct zpci_dev *zdev = container_of(hotplug_slot, struct zpci_dev,
···
 static const struct hotplug_slot_ops s390_hotplug_slot_ops = {
 	.enable_slot =		enable_slot,
 	.disable_slot =		disable_slot,
+	.reset_slot =		reset_slot,
 	.get_power_status =	get_power_status,
 	.get_adapter_status =	get_adapter_status,
 };