linux-kernel - [PATCH v2] PCI/DPC: Fix PCI legacy interrupt acknowledgement

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Date:   Wed, 14 Mar 2018 21:20:48 +0530
From:   Oza Pawandeep <poza@...eaurora.org>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dongdong Liu <liudongdong3@...wei.com>,
        Keith Busch <keith.busch@...el.com>, Wei Zhang <wzhang@...com>,
        Sinan Kaya <okaya@...eaurora.org>,
        Timur Tabi <timur@...eaurora.org>
Cc:     Oza Pawandeep <poza@...eaurora.org>
Subject: [PATCH v2] PCI/DPC: Fix PCI legacy interrupt acknowledgement

Current DPC driver acknowledges the interrupt in deferred work, which works
since MSI are edge triggered.

But when MSI is disabled (e.g. pci=nomsi boot option) port service
driver falls back to PCI legacy INT interrupt.

With current code we do not acknowledge the interrupt back in dpc_irq()
and we get dpc interrupt storm.

This patch acknowledges the interrupt in interrupt handler.

Signed-off-by: Oza Pawandeep <poza@...eaurora.org>

diff --git a/drivers/pci/pcie/pcie-dpc.c b/drivers/pci/pcie/pcie-dpc.c
index 38e40c6..9c05120 100644
--- a/drivers/pci/pcie/pcie-dpc.c
+++ b/drivers/pci/pcie/pcie-dpc.c
@@ -112,7 +112,7 @@ static void dpc_work(struct work_struct *work)
 	}
 
 	pci_write_config_word(pdev, cap + PCI_EXP_DPC_STATUS,
-		PCI_EXP_DPC_STATUS_TRIGGER | PCI_EXP_DPC_STATUS_INTERRUPT);
+			      PCI_EXP_DPC_STATUS_TRIGGER);
 
 	pci_read_config_word(pdev, cap + PCI_EXP_DPC_CTL, &ctl);
 	pci_write_config_word(pdev, cap + PCI_EXP_DPC_CTL,
@@ -222,6 +222,9 @@ static irqreturn_t dpc_irq(int irq, void *context)
 	if (dpc->rp_extensions && reason == 3 && ext_reason == 0)
 		dpc_process_rp_pio_error(dpc);
 
+	pci_write_config_word(pdev, cap + PCI_EXP_DPC_STATUS,
+			      PCI_EXP_DPC_STATUS_INTERRUPT);
+
 	schedule_work(&dpc->work);
 
 	return IRQ_HANDLED;
-- 
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a Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.