cxl: Add cxl_check_and_switch_mode() API to switch bi-modal cards

Add a new API, cxl_check_and_switch_mode() to allow for switching of
bi-modal CAPI cards, such as the Mellanox CX-4 network card.

When a driver requests to switch a card to CAPI mode, use PCI hotplug
infrastructure to remove all PCI devices underneath the slot. We then write
an updated mode control register to the CAPI VSEC, hot reset the card, and
reprobe the card.

As the card may present a different set of PCI devices after the mode
switch, use the infrastructure provided by the pnv_php driver and the OPAL
PCI slot management facilities to ensure that:

  * the old devices are removed from both the OPAL and Linux device trees
  * the new devices are probed by OPAL and added to the OPAL device tree
  * the new devices are added to the Linux device tree and probed through
    the regular PCI device probe path

As such, introduce a new option, CONFIG_CXL_BIMODAL, with a dependency on
the pnv_php driver.

Refactor existing code that touches the mode control register in the
regular single mode case into a new function, setup_cxl_protocol_area().
Co-authored-by: Ian Munsie <imunsie@au1.ibm.com>
Cc: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/Kconfig

@@ -38,3 +38,11 @@ config CXL
 	  CAPI adapters are found in POWER8 based systems.
 
 	  If unsure, say N.
+
+config CXL_BIMODAL
+	bool "Support for bi-modal CAPI cards"
+	depends on HOTPLUG_PCI_POWERNV = y && CXL || HOTPLUG_PCI_POWERNV = m && CXL = m
+	default y
+	help
+	  Select this option to enable support for bi-modal CAPI cards, such as
+	  the Mellanox CX-4.

drivers/misc/cxl/pci.c

@@ -55,6 +55,8 @@
 	pci_read_config_byte(dev, vsec + 0xa, dest)
 #define CXL_WRITE_VSEC_MODE_CONTROL(dev, vsec, val) \
 	pci_write_config_byte(dev, vsec + 0xa, val)
+#define CXL_WRITE_VSEC_MODE_CONTROL_BUS(bus, devfn, vsec, val) \
+	pci_bus_write_config_byte(bus, devfn, vsec + 0xa, val)
 #define CXL_VSEC_PROTOCOL_MASK   0xe0
 #define CXL_VSEC_PROTOCOL_1024TB 0x80
 #define CXL_VSEC_PROTOCOL_512TB  0x40
@@ -614,37 +616,235 @@ static int setup_cxl_bars(struct pci_dev *dev)
 	return 0;
 }
 
-/* pciex node: ibm,opal-m64-window = <0x3d058 0x0 0x3d058 0x0 0x8 0x0>; */
-static int switch_card_to_cxl(struct pci_dev *dev)
-{
+#ifdef CONFIG_CXL_BIMODAL
+
+struct cxl_switch_work {
+	struct pci_dev *dev;
+	struct work_struct work;
 	int vsec;
+	int mode;
+};
+
+static void switch_card_to_cxl(struct work_struct *work)
+{
+	struct cxl_switch_work *switch_work =
+		container_of(work, struct cxl_switch_work, work);
+	struct pci_dev *dev = switch_work->dev;
+	struct pci_bus *bus = dev->bus;
+	struct pci_controller *hose = pci_bus_to_host(bus);
+	struct pci_dev *bridge;
+	struct pnv_php_slot *php_slot;
+	unsigned int devfn;
 	u8 val;
 	int rc;
 
-	dev_info(&dev->dev, "switch card to CXL\n");
+	dev_info(&bus->dev, "cxl: Preparing for mode switch...\n");
+	bridge = list_first_entry_or_null(&hose->bus->devices, struct pci_dev,
+					  bus_list);
+	if (!bridge) {
+		dev_WARN(&bus->dev, "cxl: Couldn't find root port!\n");
+		goto err_dev_put;
+	}
 
-	if (!(vsec = find_cxl_vsec(dev))) {
-		dev_err(&dev->dev, "ABORTING: CXL VSEC not found!\n");
-		return -ENODEV;
+	php_slot = pnv_php_find_slot(pci_device_to_OF_node(bridge));
+	if (!php_slot) {
+		dev_err(&bus->dev, "cxl: Failed to find slot hotplug "
+			           "information. You may need to upgrade "
+			           "skiboot. Aborting.\n");
+		goto err_dev_put;
 	}
 
-	if ((rc = CXL_READ_VSEC_MODE_CONTROL(dev, vsec, &val))) {
-		dev_err(&dev->dev, "failed to read current mode control: %i", rc);
-		return rc;
+	rc = CXL_READ_VSEC_MODE_CONTROL(dev, switch_work->vsec, &val);
+	if (rc) {
+		dev_err(&bus->dev, "cxl: Failed to read CAPI mode control: %i\n", rc);
+		goto err_dev_put;
 	}
+	devfn = dev->devfn;
+
+	/* Release the reference obtained in cxl_check_and_switch_mode() */
+	pci_dev_put(dev);
+
+	dev_dbg(&bus->dev, "cxl: Removing PCI devices from kernel\n");
+	pci_lock_rescan_remove();
+	pci_hp_remove_devices(bridge->subordinate);
+	pci_unlock_rescan_remove();
+
+	/* Switch the CXL protocol on the card */
+	if (switch_work->mode == CXL_BIMODE_CXL) {
+		dev_info(&bus->dev, "cxl: Switching card to CXL mode\n");
 		val &= ~CXL_VSEC_PROTOCOL_MASK;
 		val |= CXL_VSEC_PROTOCOL_256TB | CXL_VSEC_PROTOCOL_ENABLE;
-	if ((rc = CXL_WRITE_VSEC_MODE_CONTROL(dev, vsec, val))) {
-		dev_err(&dev->dev, "failed to enable CXL protocol: %i", rc);
-		return rc;
+		rc = pnv_cxl_enable_phb_kernel_api(hose, true);
+		if (rc) {
+			dev_err(&bus->dev, "cxl: Failed to enable kernel API"
+				           " on real PHB, aborting\n");
+			goto err_free_work;
+		}
+	} else {
+		dev_WARN(&bus->dev, "cxl: Switching card to PCI mode not supported!\n");
+		goto err_free_work;
 	}
+
+	rc = CXL_WRITE_VSEC_MODE_CONTROL_BUS(bus, devfn, switch_work->vsec, val);
+	if (rc) {
+		dev_err(&bus->dev, "cxl: Failed to configure CXL protocol: %i\n", rc);
+		goto err_free_work;
+	}
+
 	/*
-	 * The CAIA spec (v0.12 11.6 Bi-modal Device Support) states
-	 * we must wait 100ms after this mode switch before touching
-	 * PCIe config space.
+	 * The CAIA spec (v1.1, Section 10.6 Bi-modal Device Support) states
+	 * we must wait 100ms after this mode switch before touching PCIe config
+	 * space.
 	 */
 	msleep(100);
 
+	/*
+	 * Hot reset to cause the card to come back in cxl mode. A
+	 * OPAL_RESET_PCI_LINK would be sufficient, but currently lacks support
+	 * in skiboot, so we use a hot reset instead.
+	 *
+	 * We call pci_set_pcie_reset_state() on the bridge, as a CAPI card is
+	 * guaranteed to sit directly under the root port, and setting the reset
+	 * state on a device directly under the root port is equivalent to doing
+	 * it on the root port iself.
+	 */
+	dev_info(&bus->dev, "cxl: Configuration write complete, resetting card\n");
+	pci_set_pcie_reset_state(bridge, pcie_hot_reset);
+	pci_set_pcie_reset_state(bridge, pcie_deassert_reset);
+
+	dev_dbg(&bus->dev, "cxl: Offlining slot\n");
+	rc = pnv_php_set_slot_power_state(&php_slot->slot, OPAL_PCI_SLOT_OFFLINE);
+	if (rc) {
+		dev_err(&bus->dev, "cxl: OPAL offlining call failed: %i\n", rc);
+		goto err_free_work;
+	}
+
+	dev_dbg(&bus->dev, "cxl: Onlining and probing slot\n");
+	rc = pnv_php_set_slot_power_state(&php_slot->slot, OPAL_PCI_SLOT_ONLINE);
+	if (rc) {
+		dev_err(&bus->dev, "cxl: OPAL onlining call failed: %i\n", rc);
+		goto err_free_work;
+	}
+
+	pci_lock_rescan_remove();
+	pci_hp_add_devices(bridge->subordinate);
+	pci_unlock_rescan_remove();
+
+	dev_info(&bus->dev, "cxl: CAPI mode switch completed\n");
+	kfree(switch_work);
+	return;
+
+err_dev_put:
+	/* Release the reference obtained in cxl_check_and_switch_mode() */
+	pci_dev_put(dev);
+err_free_work:
+	kfree(switch_work);
+}
+
+int cxl_check_and_switch_mode(struct pci_dev *dev, int mode, int vsec)
+{
+	struct cxl_switch_work *work;
+	u8 val;
+	int rc;
+
+	if (!cpu_has_feature(CPU_FTR_HVMODE))
+		return -ENODEV;
+
+	if (!vsec) {
+		vsec = find_cxl_vsec(dev);
+		if (!vsec) {
+			dev_info(&dev->dev, "CXL VSEC not found\n");
+			return -ENODEV;
+		}
+	}
+
+	rc = CXL_READ_VSEC_MODE_CONTROL(dev, vsec, &val);
+	if (rc) {
+		dev_err(&dev->dev, "Failed to read current mode control: %i", rc);
+		return rc;
+	}
+
+	if (mode == CXL_BIMODE_PCI) {
+		if (!(val & CXL_VSEC_PROTOCOL_ENABLE)) {
+			dev_info(&dev->dev, "Card is already in PCI mode\n");
+			return 0;
+		}
+		/*
+		 * TODO: Before it's safe to switch the card back to PCI mode
+		 * we need to disable the CAPP and make sure any cachelines the
+		 * card holds have been flushed out. Needs skiboot support.
+		 */
+		dev_WARN(&dev->dev, "CXL mode switch to PCI unsupported!\n");
+		return -EIO;
+	}
+
+	if (val & CXL_VSEC_PROTOCOL_ENABLE) {
+		dev_info(&dev->dev, "Card is already in CXL mode\n");
+		return 0;
+	}
+
+	dev_info(&dev->dev, "Card is in PCI mode, scheduling kernel thread "
+			    "to switch to CXL mode\n");
+
+	work = kmalloc(sizeof(struct cxl_switch_work), GFP_KERNEL);
+	if (!work)
+		return -ENOMEM;
+
+	pci_dev_get(dev);
+	work->dev = dev;
+	work->vsec = vsec;
+	work->mode = mode;
+	INIT_WORK(&work->work, switch_card_to_cxl);
+
+	schedule_work(&work->work);
+
+	/*
+	 * We return a failure now to abort the driver init. Once the
+	 * link has been cycled and the card is in cxl mode we will
+	 * come back (possibly using the generic cxl driver), but
+	 * return success as the card should then be in cxl mode.
+	 *
+	 * TODO: What if the card comes back in PCI mode even after
+	 *       the switch?  Don't want to spin endlessly.
+	 */
+	return -EBUSY;
+}
+EXPORT_SYMBOL_GPL(cxl_check_and_switch_mode);
+
+#endif /* CONFIG_CXL_BIMODAL */
+
+static int setup_cxl_protocol_area(struct pci_dev *dev)
+{
+	u8 val;
+	int rc;
+	int vsec = find_cxl_vsec(dev);
+
+	if (!vsec) {
+		dev_info(&dev->dev, "CXL VSEC not found\n");
+		return -ENODEV;
+	}
+
+	rc = CXL_READ_VSEC_MODE_CONTROL(dev, vsec, &val);
+	if (rc) {
+		dev_err(&dev->dev, "Failed to read current mode control: %i\n", rc);
+		return rc;
+	}
+
+	if (!(val & CXL_VSEC_PROTOCOL_ENABLE)) {
+		dev_err(&dev->dev, "Card not in CAPI mode!\n");
+		return -EIO;
+	}
+
+	if ((val & CXL_VSEC_PROTOCOL_MASK) != CXL_VSEC_PROTOCOL_256TB) {
+		val &= ~CXL_VSEC_PROTOCOL_MASK;
+		val |= CXL_VSEC_PROTOCOL_256TB;
+		rc = CXL_WRITE_VSEC_MODE_CONTROL(dev, vsec, val);
+		if (rc) {
+			dev_err(&dev->dev, "Failed to set CXL protocol area: %i\n", rc);
+			return rc;
+		}
+	}
+
 	return 0;
 }
 
@@ -1249,7 +1449,7 @@ static int cxl_configure_adapter(struct cxl *adapter, struct pci_dev *dev)
 	if ((rc = setup_cxl_bars(dev)))
 		return rc;
 
-	if ((rc = switch_card_to_cxl(dev)))
+	if ((rc = setup_cxl_protocol_area(dev)))
 		return rc;
 
 	if ((rc = cxl_update_image_control(adapter)))

include/misc/cxl.h

@@ -39,6 +39,31 @@
 bool cxl_slot_is_supported(struct pci_dev *dev, int flags);
 
 
+#define CXL_BIMODE_CXL 1
+#define CXL_BIMODE_PCI 2
+
+/*
+ * Check the mode that the given bi-modal CXL adapter is currently in and
+ * change it if necessary. This does not apply to AFU drivers.
+ *
+ * If the mode matches the requested mode this function will return 0 - if the
+ * driver was expecting the generic CXL driver to have bound to the adapter and
+ * it gets this return value it should fail the probe function to give the CXL
+ * driver a chance to probe it.
+ *
+ * If the mode does not match it will start a background task to unplug the
+ * device from Linux and switch its mode, and will return -EBUSY. At this
+ * point the calling driver should make sure it has released the device and
+ * fail its probe function.
+ *
+ * The offset of the CXL VSEC can be provided to this function. If 0 is passed,
+ * this function will search for a CXL VSEC with ID 0x1280 and return -ENODEV
+ * if it is not found.
+ */
+#ifdef CONFIG_CXL_BIMODAL
+int cxl_check_and_switch_mode(struct pci_dev *dev, int mode, int vsec);
+#endif
+
 /* Get the AFU associated with a pci_dev */
 struct cxl_afu *cxl_pci_to_afu(struct pci_dev *dev);