staging: mt7621-pci: fix hang when nothing is connected to pcie ports

commit 7d761b0 upstream.

When nothing is connected to pcie ports, each port is set to reset state.
When this occurs, next access result in a hang on boot as follows:

mt7621-pci 1e140000.pcie: pcie0 no card, disable it (RST & CLK)
mt7621-pci 1e140000.pcie: pcie1 no card, disable it (RST & CLK)
mt7621-pci 1e140000.pcie: pcie2 no card, disable it (RST & CLK)
[ HANGS HERE ]

Fix this just detecting 'nothing is connected state' to avoid next accesses
to pcie port related configuration registers.

Fixes: b99cc3a ("staging: mt7621-pci: avoid custom 'map_irq' function")
Cc: stable <stable@vger.kernel.org>
Reported-by: DENG Qingfang <dqfext@gmail.com>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210823170803.2108-1-sergio.paracuellos@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-pci/pci-mt7621.c

@@ -56,6 +56,7 @@
 #define PCIE_BAR_ENABLE			BIT(0)
 #define PCIE_PORT_INT_EN(x)		BIT(20 + (x))
 #define PCIE_PORT_LINKUP		BIT(0)
+#define PCIE_PORT_CNT			3
 
 #define PERST_DELAY_MS			100
 
@@ -388,10 +389,11 @@ static void mt7621_pcie_reset_ep_deassert(struct mt7621_pcie *pcie)
 	msleep(PERST_DELAY_MS);
 }
 
-static void mt7621_pcie_init_ports(struct mt7621_pcie *pcie)
+static int mt7621_pcie_init_ports(struct mt7621_pcie *pcie)
 {
 	struct device *dev = pcie->dev;
 	struct mt7621_pcie_port *port, *tmp;
+	u8 num_disabled = 0;
 	int err;
 
 	mt7621_pcie_reset_assert(pcie);
@@ -423,6 +425,7 @@ static void mt7621_pcie_init_ports(struct mt7621_pcie *pcie)
 				slot);
 			mt7621_control_assert(port);
 			port->enabled = false;
+			num_disabled++;
 
 			if (slot == 0) {
 				tmp = port;
@@ -433,6 +436,8 @@ static void mt7621_pcie_init_ports(struct mt7621_pcie *pcie)
 				phy_power_off(tmp->phy);
 		}
 	}
+
+	return (num_disabled != PCIE_PORT_CNT) ? 0 : -ENODEV;
 }
 
 static void mt7621_pcie_enable_port(struct mt7621_pcie_port *port)
@@ -540,7 +545,11 @@ static int mt7621_pci_probe(struct platform_device *pdev)
 		return err;
 	}
 
-	mt7621_pcie_init_ports(pcie);
+	err = mt7621_pcie_init_ports(pcie);
+	if (err) {
+		dev_err(dev, "Nothing connected in virtual bridges\n");
+		return 0;
+	}
 
 	err = mt7621_pcie_enable_ports(bridge);
 	if (err) {