PCI: mediatek: Clear interrupt status before dispatching handler

We found a failure when using the iperf tool during WiFi performance
testing, where some MSIs were received while clearing the interrupt
status, and these MSIs cannot be serviced.

The interrupt status can be cleared even if the MSI status remains pending.
As such, given the edge-triggered interrupt type, its status should be
cleared before being dispatched to the handler of the underling device.

[kwilczynski: commit log, code comment wording]
Link: https://lore.kernel.org/linux-pci/[email protected]
Fixes: 43e6409 ("PCI: mediatek: Add MSI support for MT2712 and MT7622")
Signed-off-by: qizhong cheng <[email protected]>
Signed-off-by: Jianjun Wang <[email protected]>
Signed-off-by: Krzysztof Wilczyński <[email protected]>
[bhelgaas: rewrap comment]
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Cc:  <[email protected]>

Author: mtk20626

drivers/pci/controller/pcie-mediatek.c

@@ -617,12 +617,18 @@ static void mtk_pcie_intr_handler(struct irq_desc *desc)
 		if (status & MSI_STATUS){
 			unsigned long imsi_status;
 
+			/*
+			 * The interrupt status can be cleared even if the
+			 * MSI status remains pending. As such, given the
+			 * edge-triggered interrupt type, its status should
+			 * be cleared before being dispatched to the
+			 * handler of the underlying device.
+			 */
+			writel(MSI_STATUS, port->base + PCIE_INT_STATUS);
 			while ((imsi_status = readl(port->base + PCIE_IMSI_STATUS))) {
 				for_each_set_bit(bit, &imsi_status, MTK_MSI_IRQS_NUM)
 					generic_handle_domain_irq(port->inner_domain, bit);
 			}
-			/* Clear MSI interrupt status */
-			writel(MSI_STATUS, port->base + PCIE_INT_STATUS);
 		}
 	}