[PATCH v8 3/9] PCI: tegra194: Remove IRQF_ONESHOT flag during Endpoint interrupt registration

[Manikanta Maddireddy]

From: Vidya Sagar <vidyas@xxxxxxxxxx>

The Tegra PCIe Endpoint controller has a single interrupt line that is
shared between multiple interrupt sources:
1. PCIe link state events (link up, hot reset done)
2. Configuration space events (Bus Master Enable changes)
3. DMA completion events

The interrupt is currently registered with IRQF_ONESHOT, which keeps the
interrupt line masked until the threaded handler completes. That blocks
processing of DMA completion events (and other sources) while the
threaded handler runs.

Removing IRQF_ONESHOT is safe for the following reasons:

1. The hard IRQ handler (tegra_pcie_ep_hard_irq) properly acknowledges and
   clears all interrupt status bits in hardware before returning. This
   prevents interrupt storms and ensures the interrupt controller can
   re-enable the interrupt line immediately.

2. A follow-up patch adds handling in the hard IRQ for DMA completion
   events. Dropping IRQF_ONESHOT is required so the line is unmasked
   after the hard IRQ returns and those events can be serviced without
   being blocked by the threaded handler.

3. The threaded handler (tegra_pcie_ep_irq_thread) only processes link-up
   notifications and LTR message sending. These operations don't conflict
   with DMA interrupt processing and don't require the interrupt line to
   remain masked.

This change enables both DMA driver and Endpoint controller driver to share
the interrupt line without blocking each other.

Reviewed-by: Jon Hunter <jonathanh@xxxxxxxxxx>
Tested-by: Jon Hunter <jonathanh@xxxxxxxxxx>
Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
Signed-off-by: Manikanta Maddireddy <mmaddireddy@xxxxxxxxxx>
---
Changes V8: Fix commit message
Changes V6 -> V7: None
Changes V1 -> V6: Updated commit message

 drivers/pci/controller/dwc/pcie-tegra194.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
index 37fcac55838f..63173f7af62b 100644
--- a/drivers/pci/controller/dwc/pcie-tegra194.c
+++ b/drivers/pci/controller/dwc/pcie-tegra194.c
@@ -2243,7 +2243,7 @@ static int tegra_pcie_dw_probe(struct platform_device *pdev)
 		ret = devm_request_threaded_irq(dev, pp->irq,
 						tegra_pcie_ep_hard_irq,
 						tegra_pcie_ep_irq_thread,
-						IRQF_SHARED | IRQF_ONESHOT,
+						IRQF_SHARED,
 						"tegra-pcie-ep-intr", pcie);
 		if (ret) {
 			dev_err(dev, "Failed to request IRQ %d: %d\n", pp->irq,
-- 
2.34.1