PCI: mvebu: Fix support for PCI_EXP_RTSTA on emulated bridge

PME Status bit in Root Status Register (PCIE_RC_RTSTA_OFF) is read-only and
can be cleared only by writing 0b to the Interrupt Cause RW0C register
(PCIE_INT_CAUSE_OFF).

Link: https://lore.kernel.org/r/20211125124605.25915-15-pali@kernel.org
Fixes: 1f08673e ("PCI: mvebu: Convert to PCI emulated bridge config space")
Signed-off-by: NPali Rohár <pali@kernel.org>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>

drivers/pci/controller/pci-mvebu.c

@@ -51,6 +51,8 @@
 	 PCIE_CONF_FUNC(PCI_FUNC(devfn)) | PCIE_CONF_REG(where) | \
 	 PCIE_CONF_ADDR_EN)
 #define PCIE_CONF_DATA_OFF	0x18fc
+#define PCIE_INT_CAUSE_OFF	0x1900
+#define  PCIE_INT_PM_PME		BIT(28)
 #define PCIE_MASK_OFF		0x1910
 #define  PCIE_MASK_ENABLE_INTS          0x0f000000
 #define PCIE_CTRL_OFF		0x1a00
@@ -661,7 +663,14 @@ mvebu_pci_bridge_emul_pcie_conf_write(struct pci_bridge_emul *bridge,
 		break;
 
 	case PCI_EXP_RTSTA:
-		mvebu_writel(port, new, PCIE_RC_RTSTA);
+		/*
+		 * PME Status bit in Root Status Register (PCIE_RC_RTSTA)
+		 * is read-only and can be cleared only by writing 0b to the
+		 * Interrupt Cause RW0C register (PCIE_INT_CAUSE_OFF). So
+		 * clear PME via Interrupt Cause.
+		 */
+		if (new & PCI_EXP_RTSTA_PME)
+			mvebu_writel(port, ~PCIE_INT_PM_PME, PCIE_INT_CAUSE_OFF);
 		break;
 	}
 }