powerpc/powernv: Add ppc_pci_reset_phbs parameter to issue a PHB reset

During a kdump kernel boot in PowerPC, we request a reset of the PHBs
to the FW. It makes sense, since if we are booting a kdump kernel it
means we had some trouble before and we cannot rely in the adapters'
health; they could be in a bad state, hence the reset is needed.

But this reset is useful not only in kdump - there are situations,
specially when debugging drivers, that we could break an adapter in
a way it requires such reset. One can tell to just go ahead and
reboot the machine, but happens that many times doing kexec is much
faster, and so preferable than a full power cycle.

This patch adds the ppc_pci_reset_phbs parameter to perform such reset.
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/pci-ioda.c

@@ -89,6 +89,7 @@ void pe_level_printk(const struct pnv_ioda_pe *pe, const char *level,
 }
 
 static bool pnv_iommu_bypass_disabled __read_mostly;
+static bool pci_reset_phbs __read_mostly;
 
 static int __init iommu_setup(char *str)
 {
@@ -110,6 +111,14 @@ static int __init iommu_setup(char *str)
 }
 early_param("iommu", iommu_setup);
 
+static int __init pci_reset_phbs_setup(char *str)
+{
+	pci_reset_phbs = true;
+	return 0;
+}
+
+early_param("ppc_pci_reset_phbs", pci_reset_phbs_setup);
+
 static inline bool pnv_pci_is_m64(struct pnv_phb *phb, struct resource *r)
 {
 	/*
@@ -4033,9 +4042,10 @@ static void __init pnv_pci_init_ioda_phb(struct device_node *np,
 	 * If we're running in kdump kernel, the previous kernel never
 	 * shutdown PCI devices correctly. We already got IODA table
 	 * cleaned out. So we have to issue PHB reset to stop all PCI
-	 * transactions from previous kernel.
+	 * transactions from previous kernel. The ppc_pci_reset_phbs
+	 * kernel parameter will force this reset too.
 	 */
-	if (is_kdump_kernel()) {
+	if (is_kdump_kernel() || pci_reset_phbs) {
 		pr_info("  Issue PHB reset ...\n");
 		pnv_eeh_phb_reset(hose, EEH_RESET_FUNDAMENTAL);
 		pnv_eeh_phb_reset(hose, EEH_RESET_DEACTIVATE);