MIPS: pci-rt2880: fix slot 0 configuration

pci_fixup_irqs() used to call pcibios_map_irq on every PCI device, which
for RT2880 included bus 0 slot 0. After pci_fixup_irqs() got removed,
only slots/funcs with devices attached would be called. While arguably
the right thing, that left no chance for this driver to ever initialize
slot 0, effectively bricking PCI and USB on RT2880 devices such as the
Belkin F5D8235-4 v1.

Slot 0 configuration needs to happen after PCI bus enumeration, but
before any device at slot 0x11 (func 0 or 1) is talked to. That was
determined empirically by testing on a Belkin F5D8235-4 v1 device. A
minimal BAR 0 config write followed by read, then setting slot 0
PCI_COMMAND to MASTER | IO | MEMORY is all that seems to be required for
proper functionality.

Tested by ensuring that full- and high-speed USB devices get enumerated
on the Belkin F5D8235-4 v1 (with an out of tree DTS file from OpenWrt).

Fixes: 04c81c72 ("MIPS: PCI: Replace pci_fixup_irqs() call with host bridge IRQ mapping hooks")
Signed-off-by: NIlya Lipnitskiy <ilya.lipnitskiy@gmail.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Tobias Wolf <dev-NTEO@vplace.de>
Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: NThomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/pci/pci-rt2880.c

@@ -180,7 +180,6 @@ static inline void rt2880_pci_write_u32(unsigned long reg, u32 val)
 
 int pcibios_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
 {
-	u16 cmd;
 	int irq = -1;
 
 	if (dev->bus->number != 0)
@@ -188,8 +187,6 @@ int pcibios_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
 
 	switch (PCI_SLOT(dev->devfn)) {
 	case 0x00:
-		rt2880_pci_write_u32(PCI_BASE_ADDRESS_0, 0x08000000);
-		(void) rt2880_pci_read_u32(PCI_BASE_ADDRESS_0);
 		break;
 	case 0x11:
 		irq = RT288X_CPU_IRQ_PCI;
@@ -201,16 +198,6 @@ int pcibios_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
 		break;
 	}
 
-	pci_write_config_byte((struct pci_dev *) dev,
-		PCI_CACHE_LINE_SIZE, 0x14);
-	pci_write_config_byte((struct pci_dev *) dev, PCI_LATENCY_TIMER, 0xFF);
-	pci_read_config_word((struct pci_dev *) dev, PCI_COMMAND, &cmd);
-	cmd |= PCI_COMMAND_MASTER | PCI_COMMAND_IO | PCI_COMMAND_MEMORY |
-		PCI_COMMAND_INVALIDATE | PCI_COMMAND_FAST_BACK |
-		PCI_COMMAND_SERR | PCI_COMMAND_WAIT | PCI_COMMAND_PARITY;
-	pci_write_config_word((struct pci_dev *) dev, PCI_COMMAND, cmd);
-	pci_write_config_byte((struct pci_dev *) dev, PCI_INTERRUPT_LINE,
-			      dev->irq);
 	return irq;
 }
 
@@ -251,6 +238,30 @@ static int rt288x_pci_probe(struct platform_device *pdev)
 
 int pcibios_plat_dev_init(struct pci_dev *dev)
 {
+	static bool slot0_init;
+
+	/*
+	 * Nobody seems to initialize slot 0, but this platform requires it, so
+	 * do it once when some other slot is being enabled. The PCI subsystem
+	 * should configure other slots properly, so no need to do anything
+	 * special for those.
+	 */
+	if (!slot0_init && dev->bus->number == 0) {
+		u16 cmd;
+		u32 bar0;
+
+		slot0_init = true;
+
+		pci_bus_write_config_dword(dev->bus, 0, PCI_BASE_ADDRESS_0,
+					   0x08000000);
+		pci_bus_read_config_dword(dev->bus, 0, PCI_BASE_ADDRESS_0,
+					  &bar0);
+
+		pci_bus_read_config_word(dev->bus, 0, PCI_COMMAND, &cmd);
+		cmd |= PCI_COMMAND_MASTER | PCI_COMMAND_IO | PCI_COMMAND_MEMORY;
+		pci_bus_write_config_word(dev->bus, 0, PCI_COMMAND, cmd);
+	}
+
 	return 0;
 }