[PATCH 1/2] PCI/DPC: Clear Interrupt Status in dpc_reset_link()

[Danielle Costantino <dcostantino@meta.com>]

In the native DPC interrupt path, dpc_irq() clears
PCI_EXP_DPC_STATUS_INTERRUPT before scheduling the threaded handler
that eventually calls dpc_reset_link().  However, in the firmware-first
EDR path, dpc_irq() is never invoked -- firmware owns the DPC interrupt
and notifies the OS via an ACPI EDR notification.  dpc_reset_link() is
then called directly from edr_handle_event() via pcie_do_recovery().

Because dpc_reset_link() only clears PCI_EXP_DPC_STATUS_TRIGGER, the
Interrupt Status bit (bit 3) is left set permanently after every EDR
event.

Clear PCI_EXP_DPC_STATUS_INTERRUPT alongside PCI_EXP_DPC_STATUS_TRIGGER
in dpc_reset_link().  Both bits are RW1C in the DPC Status register per
PCIe r6.1, sec 7.9.14.5, so writing them together is safe.  The native
path is unaffected because dpc_irq() has already cleared the Interrupt
Status bit before dpc_reset_link() runs.

Fixes: aea47413e7ce ("PCI/DPC: Expose dpc_process_error(), dpc_reset_link() for use by EDR")
Signed-off-by: Danielle Costantino <dcostantino@meta.com>
---
 drivers/pci/pcie/dpc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
index fc18349614d7..9baa2345e33e 100644
--- a/drivers/pci/pcie/dpc.c
+++ b/drivers/pci/pcie/dpc.c
@@ -171,8 +171,16 @@ pci_ers_result_t dpc_reset_link(struct pci_dev *pdev)
 		goto out;
 	}
 
+	/*
+	 * Clear both DPC Trigger Status and DPC Interrupt Status.  In the
+	 * native DPC path, dpc_irq() already clears Interrupt Status before
+	 * the threaded handler runs.  But in the EDR (firmware-first) path,
+	 * dpc_irq() is never called, so Interrupt Status must be cleared
+	 * here to prevent it from remaining stale indefinitely.
+	 */
 	pci_write_config_word(pdev, cap + PCI_EXP_DPC_STATUS,
-			      PCI_EXP_DPC_STATUS_TRIGGER);
+			      PCI_EXP_DPC_STATUS_TRIGGER |
+			      PCI_EXP_DPC_STATUS_INTERRUPT);
 
 	if (pci_bridge_wait_for_secondary_bus(pdev, "DPC")) {
 		clear_bit(PCI_DPC_RECOVERED, &pdev->priv_flags);
-- 
2.47.3