PCI: tegra: Process pending DLL transactions before entering L1 or L2

PM message are truncated while entering L1 or L2, which is resulting in
receiver errors. Set the required bit to finish processing DLLP before
link enter L1 or L2.
Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Thierry Reding <treding@nvidia.com>

drivers/pci/controller/pci-tegra.c

@@ -212,6 +212,9 @@
 #define RP_VEND_CTL1	0x00000f48
 #define  RP_VEND_CTL1_ERPT	(1 << 13)
 
+#define RP_VEND_XP_BIST	0x00000f4c
+#define  RP_VEND_XP_BIST_GOTO_L1_L2_AFTER_DLLP_DONE	(1 << 28)
+
 #define RP_VEND_CTL2 0x00000fa8
 #define  RP_VEND_CTL2_PCA_ENABLE (1 << 7)
 
@@ -538,6 +541,14 @@ static void tegra_pcie_enable_rp_features(struct tegra_pcie_port *port)
 	value |= RP_VEND_XP_OPPORTUNISTIC_ACK;
 	value |= RP_VEND_XP_OPPORTUNISTIC_UPDATEFC;
 	writel(value, port->base + RP_VEND_XP);
+
+	/*
+	 * LTSSM will wait for DLLP to finish before entering L1 or L2,
+	 * to avoid truncation of PM messages which results in receiver errors
+	 */
+	value = readl(port->base + RP_VEND_XP_BIST);
+	value |= RP_VEND_XP_BIST_GOTO_L1_L2_AFTER_DLLP_DONE;
+	writel(value, port->base + RP_VEND_XP_BIST);
 }
 
 static void tegra_pcie_program_ectl_settings(struct tegra_pcie_port *port)