PCI: imx6: Install the fault handler only on compatible match

commit bb38919e ("PCI: imx6: Add support for i.MX6 PCIe controller")
added a fault hook to this driver in the probe function. So it was only
installed if needed.

commit bde4a5a0 ("PCI: imx6: Allow probe deferral by reset GPIO")
moved it from probe to driver init which installs the hook unconditionally
as soon as the driver is compiled into a kernel.

When this driver is compiled as a module, the hook is not registered
until after the driver has been matched with a .compatible and
loaded.

commit 415b6185 ("PCI: imx6: Fix config read timeout handling")
extended the fault handling code.

commit 2d8ed461 ("PCI: imx6: Add support for i.MX8MQ")
added some protection for non-ARM architectures, but this does not
protect non-i.MX ARM architectures.

Since fault handlers can be triggered on any architecture for different
reasons, there is no guarantee that they will be triggered only for the
assumed situation, leading to improper error handling (i.MX6-specific
imx6q_pcie_abort_handler) on foreign systems.

I had seen strange L3 imprecise external abort messages several times on
OMAP4 and OMAP5 devices and couldn't make sense of them until I realized
they were related to this unused imx6q driver because I had
CONFIG_PCI_IMX6=y.

Note that CONFIG_PCI_IMX6=y is useful for kernel binaries that are designed
to run on different ARM SoC and be differentiated only by device tree
binaries. So turning off CONFIG_PCI_IMX6 is not a solution.

Therefore we check the compatible in the init function before registering
the fault handler.

Link: https://lore.kernel.org/r/e1bcfc3078c82b53aa9b78077a89955abe4ea009.1678380991.git.hns@goldelico.com
Fixes: bde4a5a0 ("PCI: imx6: Allow probe deferral by reset GPIO")
Fixes: 415b6185 ("PCI: imx6: Fix config read timeout handling")
Fixes: 2d8ed461 ("PCI: imx6: Add support for i.MX8MQ")
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Richard Zhu <hongxing.zhu@nxp.com>

drivers/pci/controller/dwc/pci-imx6.c

@@ -1566,6 +1566,13 @@ DECLARE_PCI_FIXUP_CLASS_HEADER(PCI_VENDOR_ID_SYNOPSYS, 0xabcd,
 static int __init imx6_pcie_init(void)
 {
 #ifdef CONFIG_ARM
+	struct device_node *np;
+
+	np = of_find_matching_node(NULL, imx6_pcie_of_match);
+	if (!np)
+		return -ENODEV;
+	of_node_put(np);
+
 	/*
 	 * Since probe() can be deferred we need to make sure that
 	 * hook_fault_code is not called after __init memory is freed