[PATCH] arm: a37xx: pci: Implement workaround for the readback value of VEND_ID

[Pali Rohár]

Marvell Armada 3720 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 U-Boot PCIe controller driver aardvark for
both PCI vendor id and PCI subsystem vendor id.

This change affects PCI vendor id of PCIe root bridge emulated by Linux
kernel. With this change Linux kernel reports correct vendor id 11AB.

Signed-off-by: Pali Rohár <pali at kernel.org>
---
 drivers/pci/pci-aardvark.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/pci/pci-aardvark.c b/drivers/pci/pci-aardvark.c
index b4e1b602405f..3b9309f52c57 100644
--- a/drivers/pci/pci-aardvark.c
+++ b/drivers/pci/pci-aardvark.c
@@ -105,6 +105,7 @@
 #define     LTSSM_SHIFT				24
 #define     LTSSM_MASK				0x3f
 #define     LTSSM_L0				0x10
+#define VENDOR_ID_REG				(LMI_BASE_ADDR + 0x44)
 
 /* PCIe core controller registers */
 #define CTRL_CORE_BASE_ADDR			0x18000
@@ -529,6 +530,15 @@ static int pcie_advk_setup_hw(struct pcie_advk *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".
+	 */
+	advk_writel(pcie, 0x11ab11ab, 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 |
-- 
2.20.1