Re: [PATCH v6 3/9] PCI: tegra194: Remove IRQF_ONESHOT flag during Endpoint interrupt registration

[Vidya Sagar]

On 24/02/26 00:15, Manikanta Maddireddy wrote:
> 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
> 
> Currently, the interrupt is registered with IRQF_ONESHOT, which keeps the
> interrupt line masked until the threaded handler completes. This prevents
> the DMA driver from sharing the same interrupt line, as the DMA completion
> interrupts would be blocked while the threaded handler processes link state
> events.
> 
> 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. The hard IRQ handler explicitly checks for DMA interrupts
>    (APPL_INTR_STATUS_L1_8_0_EDMA_INT_MASK) and marks them as handled,
>    allowing the DMA driver's handler to process them separately.
> 
> 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 the DMA driver to share the interrupt line with the
> PCIe endpoint driver, allowing both drivers to process their respective
> events without blocking each other.
> 
> Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> Signed-off-by: Manikanta Maddireddy <mmaddireddy@xxxxxxxxxx>
> ---
> 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 51bad99cec31..aeec5f8b9842 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -2226,7 +2226,7 @@ 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,

Reviewed-by: Vidya Sagar <vidyas@xxxxxxxxxx>