PCI: brcmstb: add NO_SSC quirk for BCM2712

The PHY MDIO register map is different on BCM2712, and as the PHY input
clock is 54MHz not 100MHz, enabling refclk SSC is both broken and
unfixable.

Mask out attempts to enable SSC with a controller quirk.

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

Author: P33M

drivers/pci/controller/pcie-brcmstb.c

@@ -259,6 +259,12 @@ struct inbound_win {
  */
 #define CFG_QUIRK_AVOID_BRIDGE_SHUTDOWN		BIT(0)
 
+/*
+ * MDIO register map differences and required changes to the defaults mean that refclk
+ * spread-spectrum clocking isn't supportable.
+ */
+#define CFG_QUIRK_NO_SSC			BIT(1)
+
 struct pcie_cfg_data {
 	const int *offsets;
 	const enum pcie_soc_base soc_base;
@@ -1811,7 +1817,7 @@ static const struct pcie_cfg_data bcm2712_cfg = {
 	.perst_set	= brcm_pcie_perst_set_7278,
 	.bridge_sw_init_set = brcm_pcie_bridge_sw_init_set_generic,
 	.post_setup	= brcm_pcie_post_setup_bcm2712,
-	.quirks		= CFG_QUIRK_AVOID_BRIDGE_SHUTDOWN,
+	.quirks		= CFG_QUIRK_AVOID_BRIDGE_SHUTDOWN | CFG_QUIRK_NO_SSC,
 	.num_inbound_wins = 10,
 };
 
@@ -1929,7 +1935,8 @@ static int brcm_pcie_probe(struct platform_device *pdev)
 	ret = of_pci_get_max_link_speed(np);
 	pcie->gen = (ret < 0) ? 0 : ret;
 
-	pcie->ssc = of_property_read_bool(np, "brcm,enable-ssc");
+	pcie->ssc = !(pcie->cfg->quirks & CFG_QUIRK_NO_SSC) &&
+		    of_property_read_bool(np, "brcm,enable-ssc");
 
 	pcie->rescal = devm_reset_control_get_optional_shared(&pdev->dev, "rescal");
 	if (IS_ERR(pcie->rescal))