powerpc/fsl-pci: Fix Class Code of PCIe Root Port

By default old pre-3.0 Freescale PCIe controllers reports invalid PCI Class
Code 0x0b20 for PCIe Root Port. It can be seen by lspci -b output on P2020
board which has this pre-3.0 controller:

  $ lspci -bvnn
  00:00.0 Power PC [0b20]: Freescale Semiconductor Inc P2020E [1957:0070] (rev 21)
          !!! Invalid class 0b20 for header type 01
          Capabilities: [4c] Express Root Port (Slot-), MSI 00

Fix this issue by programming correct PCI Class Code 0x0604 for PCIe Root
Port to the Freescale specific PCIe register 0x474.

With this change lspci -b output is:

  $ lspci -bvnn
  00:00.0 PCI bridge [0604]: Freescale Semiconductor Inc P2020E [1957:0070] (rev 21) (prog-if 00 [Normal decode])
          Capabilities: [4c] Express Root Port (Slot-), MSI 00

Without any "Invalid class" error. So class code was properly reflected
into standard (read-only) PCI register 0x08.

Same fix is already implemented in U-Boot pcie_fsl.c driver in commit:
http://source.denx.de/u-boot/u-boot/-/commit/d18d06ac35229345a0af80977a408cfbe1d1015b

Fix activated by U-Boot stay active also after booting Linux kernel.
But boards which use older U-Boot version without that fix are affected and
still require this fix.

So implement this class code fix also in kernel fsl_pci.c driver.

Cc: stable@vger.kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220706101043.4867-1-pali@kernel.org

arch/powerpc/sysdev/fsl_pci.c

@@ -522,6 +522,7 @@ int fsl_add_bridge(struct platform_device *pdev, int is_primary)
 	struct resource rsrc;
 	const int *bus_range;
 	u8 hdr_type, progif;
+	u32 class_code;
 	struct device_node *dev;
 	struct ccsr_pci __iomem *pci;
 	u16 temp;
@@ -595,6 +596,13 @@ int fsl_add_bridge(struct platform_device *pdev, int is_primary)
 			PPC_INDIRECT_TYPE_SURPRESS_PRIMARY_BUS;
 		if (fsl_pcie_check_link(hose))
 			hose->indirect_type |= PPC_INDIRECT_TYPE_NO_PCIE_LINK;
+		/* Fix Class Code to PCI_CLASS_BRIDGE_PCI_NORMAL for pre-3.0 controller */
+		if (in_be32(&pci->block_rev1) < PCIE_IP_REV_3_0) {
+			early_read_config_dword(hose, 0, 0, PCIE_FSL_CSR_CLASSCODE, &class_code);
+			class_code &= 0xff;
+			class_code |= PCI_CLASS_BRIDGE_PCI_NORMAL << 8;
+			early_write_config_dword(hose, 0, 0, PCIE_FSL_CSR_CLASSCODE, class_code);
+		}
 	} else {
 		/*
 		 * Set PBFR(PCI Bus Function Register)[10] = 1 to

arch/powerpc/sysdev/fsl_pci.h

@@ -18,6 +18,7 @@ struct platform_device;
 
 #define PCIE_LTSSM	0x0404		/* PCIE Link Training and Status */
 #define PCIE_LTSSM_L0	0x16		/* L0 state */
+#define PCIE_FSL_CSR_CLASSCODE	0x474	/* FSL GPEX CSR */
 #define PCIE_IP_REV_2_2		0x02080202 /* PCIE IP block version Rev2.2 */
 #define PCIE_IP_REV_3_0		0x02080300 /* PCIE IP block version Rev3.0 */
 #define PIWAR_EN		0x80000000	/* Enable */