Re: [PATCH v3 1/3] spi: tegra210-quad: Convert to hard IRQ with high-priority workqueue

[Mark Brown]

On Wed, May 20, 2026 at 07:24:03PM +0000, Vishwaroop A wrote:
> Threaded IRQ handlers suffer from scheduler latency on heavily loaded
> systems, causing false transfer timeouts. Convert to hard IRQ handler
> that schedules work on a high-priority unbound workqueue.

> +static void tegra_qspi_work_handler(struct work_struct *work)
>  {
> -	struct tegra_qspi *tqspi = context_data;
> +	struct tegra_qspi *tqspi = container_of(work, struct tegra_qspi, irq_work);
>  	unsigned long flags;
> -	u32 status;

> -	spin_lock_irqsave(&tqspi->lock, flags);
>  	if (!tqspi->curr_xfer) {
>  		spin_unlock_irqrestore(&tqspi->lock, flags);
> -		/* Spurious interrupt - transfer not ready */
> -		if (!(status & QSPI_RDY))
> -			return IRQ_NONE;
> -		/* Real interrupt, already handled by timeout path */
> -		return IRQ_HANDLED;
> +		tegra_qspi_unmask_irq(tqspi);
> +		return;
>  	}

What ensures that we have a runtime PM reference when this work runs?
It's also a bit odd that we unmask after dropping the lock, that feels
like it opens up races.

> +static irqreturn_t tegra_qspi_isr(int irq, void *context_data)
> +{
> +	struct tegra_qspi *tqspi = context_data;
> +	u32 status;
> +
> +	status = tegra_qspi_readl(tqspi, QSPI_TRANS_STATUS);
> +	if (!(status & QSPI_RDY))
> +		return IRQ_NONE;

Since we now have IRQF_SHARED we need to take a runtime PM reference
here, the interrupt handler could be called due to something else
sharing the interrupt lin.e

> +	ret = devm_request_irq(&pdev->dev, tqspi->irq, tegra_qspi_isr,
> +			       IRQF_SHARED, dev_name(&pdev->dev), tqspi);

> -exit_free_irq:
> -	free_irq(qspi_irq, tqspi);
>  exit_pm_disable:
>  	pm_runtime_dont_use_autosuspend(&pdev->dev);
>  	pm_runtime_force_suspend(&pdev->dev);

The use of devm for the interrupt with non-devm for other things seems
likely to be racy....

>  	spi_unregister_controller(host);
> -	free_irq(tqspi->irq, tqspi);
> +	cancel_work_sync(&tqspi->irq_work);

...especially here.

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