PCI: brcmstb: Wait for Raspberry Pi's firmware when present

xHCI's PCI fixup, run at the end of pcie-brcmstb's probe, depends on
RPi4's VideoCore firmware interface to be up and running. It's possible
for both initializations to race, so make sure it's available prior to
starting.

Link: https://lore.kernel.org/r/20200505161318.26200-4-nsaenzjulienne@suse.de
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>

drivers/pci/controller/pcie-brcmstb.c

@@ -28,6 +28,8 @@
 #include <linux/string.h>
 #include <linux/types.h>
 
+#include <soc/bcm2835/raspberrypi-firmware.h>
+
 #include "../pci.h"
 
 /* BRCM_PCIE_CAP_REGS - Offset for the mandatory capability config regs */
@@ -929,11 +931,26 @@ static int brcm_pcie_probe(struct platform_device *pdev)
 {
 	struct device_node *np = pdev->dev.of_node, *msi_np;
 	struct pci_host_bridge *bridge;
+	struct device_node *fw_np;
 	struct brcm_pcie *pcie;
 	struct pci_bus *child;
 	struct resource *res;
 	int ret;
 
+	/*
+	 * We have to wait for Raspberry Pi's firmware interface to be up as a
+	 * PCI fixup, rpi_firmware_init_vl805(), depends on it. This driver's
+	 * probe can race with the firmware interface's (see
+	 * drivers/firmware/raspberrypi.c) and potentially break the PCI fixup.
+	 */
+	fw_np = of_find_compatible_node(NULL, NULL,
+					"raspberrypi,bcm2835-firmware");
+	if (fw_np && !rpi_firmware_get(fw_np)) {
+		of_node_put(fw_np);
+		return -EPROBE_DEFER;
+	}
+	of_node_put(fw_np);
+
 	bridge = devm_pci_alloc_host_bridge(&pdev->dev, sizeof(*pcie));
 	if (!bridge)
 		return -ENOMEM;