cxl: Fix device_node reference counting

When unbinding and rebinding the driver on a system with a card in PHB0, this
error condition is reached after a few attempts:

ERROR: Bad of_node_put() on /pciex@3fffe40000000
CPU: 0 PID: 3040 Comm: bash Not tainted 3.18.0-rc3-12545-g3627ffe #152
Call Trace:
[c000000721acb5c0] [c00000000086ef94] .dump_stack+0x84/0xb0 (unreliable)
[c000000721acb640] [c00000000073a0a8] .of_node_release+0xd8/0xe0
[c000000721acb6d0] [c00000000044bc44] .kobject_release+0x74/0xe0
[c000000721acb760] [c0000000007394fc] .of_node_put+0x1c/0x30
[c000000721acb7d0] [c000000000545cd8] .cxl_probe+0x1a98/0x1d50
[c000000721acb900] [c0000000004845a0] .local_pci_probe+0x40/0xc0
[c000000721acb980] [c000000000484998] .pci_device_probe+0x128/0x170
[c000000721acba30] [c00000000052400c] .driver_probe_device+0xac/0x2a0
[c000000721acbad0] [c000000000522468] .bind_store+0x108/0x160
[c000000721acbb70] [c000000000521448] .drv_attr_store+0x38/0x60
[c000000721acbbe0] [c000000000293840] .sysfs_kf_write+0x60/0xa0
[c000000721acbc50] [c000000000292500] .kernfs_fop_write+0x140/0x1d0
[c000000721acbcf0] [c000000000208648] .vfs_write+0xd8/0x260
[c000000721acbd90] [c000000000208b18] .SyS_write+0x58/0x100
[c000000721acbe30] [c000000000009258] syscall_exit+0x0/0x98

We are missing a call to of_node_get(). pnv_pci_to_phb_node() should
call of_node_get() otherwise np's reference count isn't incremented and
it might go away. Rename pnv_pci_to_phb_node() to pnv_pci_get_phb_node()
so it's clear it calls of_node_get().

Signed-off-by: Ryan Grimm <grimm@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/pnv-pci.h

@@ -19,7 +19,7 @@ int pnv_cxl_ioda_msi_setup(struct pci_dev *dev, unsigned int hwirq,
 int pnv_cxl_alloc_hwirqs(struct pci_dev *dev, int num);
 void pnv_cxl_release_hwirqs(struct pci_dev *dev, int hwirq, int num);
 int pnv_cxl_get_irq_count(struct pci_dev *dev);
-struct device_node *pnv_pci_to_phb_node(struct pci_dev *dev);
+struct device_node *pnv_pci_get_phb_node(struct pci_dev *dev);
 
 #ifdef CONFIG_CXL_BASE
 int pnv_cxl_alloc_hwirq_ranges(struct cxl_irq_ranges *irqs,

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

@@ -1487,13 +1487,13 @@ static void set_msi_irq_chip(struct pnv_phb *phb, unsigned int virq)
 
 #ifdef CONFIG_CXL_BASE
 
-struct device_node *pnv_pci_to_phb_node(struct pci_dev *dev)
+struct device_node *pnv_pci_get_phb_node(struct pci_dev *dev)
 {
 	struct pci_controller *hose = pci_bus_to_host(dev->bus);
 
-	return hose->dn;
+	return of_node_get(hose->dn);
 }
-EXPORT_SYMBOL(pnv_pci_to_phb_node);
+EXPORT_SYMBOL(pnv_pci_get_phb_node);
 
 int pnv_phb_to_cxl_mode(struct pci_dev *dev, uint64_t mode)
 {

drivers/misc/cxl/pci.c

@@ -317,7 +317,7 @@ static int init_implementation_adapter_regs(struct cxl *adapter, struct pci_dev
 	u64 psl_dsnctl;
 	u64 chipid;
 
-	if (!(np = pnv_pci_to_phb_node(dev)))
+	if (!(np = pnv_pci_get_phb_node(dev)))
 		return -ENODEV;
 
 	while (np && !(prop = of_get_property(np, "ibm,chip-id", NULL)))