powernv/eeh: Use generic code to handle hot resets

When we reset PCI devices managed by a hotplug driver the reset may
generate spurious hotplug events that cause the PCI device we're resetting
to be torn down accidently. This is a problem for EEH (when the driver is
EEH aware) since we want to leave the OS PCI device state intact so that
the device can be re-set without losing any resources (network, disks,
etc) provided by the driver.

Generic PCI code provides the pci_bus_error_reset() function to handle
resetting a PCI Device (or bus) by using the reset method provided by the
hotplug slot driver. We can use this function if the EEH core has
requested a hot reset (common case) without tripping over the hotplug
driver.
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190903101605.2890-8-oohall@gmail.com

arch/powerpc/platforms/powernv/eeh-powernv.c

@@ -34,6 +34,7 @@
 
 #include "powernv.h"
 #include "pci.h"
+#include "../../../../drivers/pci/pci.h"
 
 static int eeh_event_irq = -EINVAL;
 
@@ -849,7 +850,7 @@ static int __pnv_eeh_bridge_reset(struct pci_dev *dev, int option)
 	int aer = edev ? edev->aer_cap : 0;
 	u32 ctrl;
 
-	pr_debug("%s: Reset PCI bus %04x:%02x with option %d\n",
+	pr_debug("%s: Secondary Reset PCI bus %04x:%02x with option %d\n",
 		 __func__, pci_domain_nr(dev->bus),
 		 dev->bus->number, option);
 
@@ -907,6 +908,10 @@ static int pnv_eeh_bridge_reset(struct pci_dev *pdev, int option)
 	if (!dn || !of_get_property(dn, "ibm,reset-by-firmware", NULL))
 		return __pnv_eeh_bridge_reset(pdev, option);
 
+	pr_debug("%s: FW reset PCI bus %04x:%02x with option %d\n",
+		 __func__, pci_domain_nr(pdev->bus),
+		 pdev->bus->number, option);
+
 	switch (option) {
 	case EEH_RESET_FUNDAMENTAL:
 		scope = OPAL_RESET_PCI_FUNDAMENTAL;
@@ -1125,10 +1130,37 @@ static int pnv_eeh_reset(struct eeh_pe *pe, int option)
 		return -EIO;
 	}
 
-	if (pci_is_root_bus(bus) ||
-	    pci_is_root_bus(bus->parent))
+	if (pci_is_root_bus(bus))
 		return pnv_eeh_root_reset(hose, option);
 
+	/*
+	 * For hot resets try use the generic PCI error recovery reset
+	 * functions. These correctly handles the case where the secondary
+	 * bus is behind a hotplug slot and it will use the slot provided
+	 * reset methods to prevent spurious hotplug events during the reset.
+	 *
+	 * Fundemental resets need to be handled internally to EEH since the
+	 * PCI core doesn't really have a concept of a fundemental reset,
+	 * mainly because there's no standard way to generate one. Only a
+	 * few devices require an FRESET so it should be fine.
+	 */
+	if (option != EEH_RESET_FUNDAMENTAL) {
+		/*
+		 * NB: Skiboot and pnv_eeh_bridge_reset() also no-op the
+		 *     de-assert step. It's like the OPAL reset API was
+		 *     poorly designed or something...
+		 */
+		if (option == EEH_RESET_DEACTIVATE)
+			return 0;
+
+		rc = pci_bus_error_reset(bus->self);
+		if (!rc)
+			return 0;
+	}
+
+	/* otherwise, use the generic bridge reset. this might call into FW */
+	if (pci_is_root_bus(bus->parent))
+		return pnv_eeh_root_reset(hose, option);
 	return pnv_eeh_bridge_reset(bus->self, option);
 }