PCI: mediatek-gen3: Print LTSSM state when PCIe link down

Print current LTSSM state when PCIe link down instead of the register
value to make it easier to get the link status.

Link: https://lore.kernel.org/r/20220329030715.7975-1-jianjun.wang@mediatek.com
Signed-off-by: Jianjun Wang <jianjun.wang@mediatek.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>

Author: wang-jianjun

drivers/pci/controller/pcie-mediatek-gen3.c

@@ -153,6 +153,37 @@ struct mtk_gen3_pcie {
 	DECLARE_BITMAP(msi_irq_in_use, PCIE_MSI_IRQS_NUM);
 };
 
+/* LTSSM state in PCIE_LTSSM_STATUS_REG bit[28:24] */
+static const char *const ltssm_str[] = {
+	"detect.quiet",			/* 0x00 */
+	"detect.active",		/* 0x01 */
+	"polling.active",		/* 0x02 */
+	"polling.compliance",		/* 0x03 */
+	"polling.configuration",	/* 0x04 */
+	"config.linkwidthstart",	/* 0x05 */
+	"config.linkwidthaccept",	/* 0x06 */
+	"config.lanenumwait",		/* 0x07 */
+	"config.lanenumaccept",		/* 0x08 */
+	"config.complete",		/* 0x09 */
+	"config.idle",			/* 0x0A */
+	"recovery.receiverlock",	/* 0x0B */
+	"recovery.equalization",	/* 0x0C */
+	"recovery.speed",		/* 0x0D */
+	"recovery.receiverconfig",	/* 0x0E */
+	"recovery.idle",		/* 0x0F */
+	"L0",				/* 0x10 */
+	"L0s",				/* 0x11 */
+	"L1.entry",			/* 0x12 */
+	"L1.idle",			/* 0x13 */
+	"L2.idle",			/* 0x14 */
+	"L2.transmitwake",		/* 0x15 */
+	"disable",			/* 0x16 */
+	"loopback.entry",		/* 0x17 */
+	"loopback.active",		/* 0x18 */
+	"loopback.exit",		/* 0x19 */
+	"hotreset",			/* 0x1A */
+};
+
 /**
  * mtk_pcie_config_tlp_header() - Configure a configuration TLP header
  * @bus: PCI bus to query
@@ -327,8 +358,16 @@ static int mtk_pcie_startup_port(struct mtk_gen3_pcie *pcie)
 				 !!(val & PCIE_PORT_LINKUP), 20,
 				 PCI_PM_D3COLD_WAIT * USEC_PER_MSEC);
 	if (err) {
+		const char *ltssm_state;
+		int ltssm_index;
+
 		val = readl_relaxed(pcie->base + PCIE_LTSSM_STATUS_REG);
-		dev_err(pcie->dev, "PCIe link down, ltssm reg val: %#x\n", val);
+		ltssm_index = PCIE_LTSSM_STATE(val);
+		ltssm_state = ltssm_index >= ARRAY_SIZE(ltssm_str) ?
+			      "Unknown state" : ltssm_str[ltssm_index];
+		dev_err(pcie->dev,
+			"PCIe link down, current LTSSM state: %s (%#x)\n",
+			ltssm_state, val);
 		return err;
 	}