PCI: aardvark: Implement workaround for the readback value of VEND_ID

Marvell Armada 3700 Functional Errata, Guidelines, and Restrictions
document describes in erratum 4.1 PCIe value of vendor ID (Ref #: 243):

    The readback value of VEND_ID (RD0070000h [15:0]) is 1B4Bh, while it
    should read 11ABh.

    The firmware can write the correct value, 11ABh, through VEND_ID
    (RD0076044h [15:0]).

Implement this workaround in aardvark driver for both PCI vendor id and PCI
subsystem vendor id.

This change affects and fixes PCI vendor id of emulated PCIe root bridge.
After this change emulated PCIe root bridge has correct vendor id.

Link: https://lore.kernel.org/r/[email protected]
Fixes: 8a3ebd8 ("PCI: aardvark: Implement emulated root PCI bridge config space")
Signed-off-by: Pali Rohár <[email protected]>
Signed-off-by: Lorenzo Pieralisi <[email protected]>
Reviewed-by: Marek Behún <[email protected]>
Cc: [email protected]

drivers/pci/controller/pci-aardvark.c

@@ -125,6 +125,7 @@
 #define     LTSSM_MASK				0x3f
 #define     LTSSM_L0				0x10
 #define     RC_BAR_CONFIG			0x300
+#define VENDOR_ID_REG				(LMI_BASE_ADDR + 0x44)
 
 /* PCIe core controller registers */
 #define CTRL_CORE_BASE_ADDR			0x18000
@@ -385,6 +386,16 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
 	reg |= (IS_RC_MSK << IS_RC_SHIFT);
 	advk_writel(pcie, reg, PCIE_CORE_CTRL0_REG);
 
+	/*
+	 * Replace incorrect PCI vendor id value 0x1b4b by correct value 0x11ab.
+	 * VENDOR_ID_REG contains vendor id in low 16 bits and subsystem vendor
+	 * id in high 16 bits. Updating this register changes readback value of
+	 * read-only vendor id bits in PCIE_CORE_DEV_ID_REG register. Workaround
+	 * for erratum 4.1: "The value of device and vendor ID is incorrect".
+	 */
+	reg = (PCI_VENDOR_ID_MARVELL << 16) | PCI_VENDOR_ID_MARVELL;
+	advk_writel(pcie, reg, VENDOR_ID_REG);
+
 	/* Set Advanced Error Capabilities and Control PF0 register */
 	reg = PCIE_CORE_ERR_CAPCTL_ECRC_CHK_TX |
 		PCIE_CORE_ERR_CAPCTL_ECRC_CHK_TX_EN |