PCI: brcmstb: Enable CRS software visibility after linkup

It appears that bits in the Root Control Register are reset with
perst_n, which means the PCI layer's call to enable CRS prior to
adding/scanning the bus has no effect. Open-code the enable in
brcm_pcie_start_link as a workaround.

Without CRS visibility, configuration reads issued by the CPU don't
retire if the endpoint returns a CRS response - the RC will poll until a
(large) timeout is reached. This means the core can stall for a long
time during boot.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>

Author: P33M

drivers/pci/controller/pcie-brcmstb.c

@@ -1358,7 +1358,7 @@ static int brcm_pcie_start_link(struct brcm_pcie *pcie)
 {
 	struct device *dev = pcie->dev;
 	void __iomem *base = pcie->base;
-	u16 nlw, cls, lnksta;
+	u16 nlw, cls, lnksta, tmp16;
 	bool ssc_good = false;
 	int ret, i;
 
@@ -1407,6 +1407,17 @@ static int brcm_pcie_start_link(struct brcm_pcie *pcie)
 		 pci_speed_string(pcie_link_speed[cls]), nlw,
 		 ssc_good ? "(SSC)" : "(!SSC)");
 
+	/*
+	 * RootCtl bits are reset by perst_n, which undoes pci_enable_crs()
+	 * called prior to pci_add_new_bus() during probe. Re-enable here.
+	 */
+	tmp16 = readw(base + BRCM_PCIE_CAP_REGS + PCI_EXP_RTCAP);
+	if (tmp16 & PCI_EXP_RTCAP_CRSVIS) {
+		tmp16 = readw(base + BRCM_PCIE_CAP_REGS + PCI_EXP_RTCTL);
+		u16p_replace_bits(&tmp16, 1, PCI_EXP_RTCTL_CRSSVE);
+		writew(tmp16, base + BRCM_PCIE_CAP_REGS + PCI_EXP_RTCTL);
+	}
+
 	return 0;
 }