[PATCH v3] PCI: mediatek: Clear interrupt status before dispatching handler

[qizhong cheng]

We found a failure when used iperf tool for wifi performance testing,
there are some MSIs received while clearing the interrupt status,
these MSIs cannot be serviced.

The interrupt status can be cleared even the MSI status still remaining,
as an edge-triggered interrupts, its interrupt status should be cleared
before dispatching to the handler of device.

Fixes: 43e6409db64d ("PCI: mediatek: Add MSI support for MT2712 and MT7622")
Signed-off-by: qizhong cheng <qizhong.cheng at mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
Cc: stable at vger.kernel.org
---

v3:
 - Add Fix tag.

v2:
 - Update the subject line.
 - Improve the commit log and code comments.

 drivers/pci/controller/pcie-mediatek.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
index 2f3f974977a3..2856d74b2513 100644
--- a/drivers/pci/controller/pcie-mediatek.c
+++ b/drivers/pci/controller/pcie-mediatek.c
@@ -624,12 +624,17 @@ 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 the MSI
+			 * status still remaining, hence as an edge-triggered
+			 * interrupts, its interrupt status should be cleared
+			 * before dispatching handler.
+			 */
+			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);
 		}
 	}
 
-- 
2.25.1