[PATCH] PCI: Mediatek: clear irq status after irq dispathed to avoid reentry

[Bjorn Helgaas]

[+cc Lorenzo, please cc him on all drivers/{host,dwc,endpoint} material]

Please run "git log --oneline drivers/pci/host/pcie-mediatek.c" and
make yours match.  Same capitalization, same sentence structure, etc.,
e.g.,

  PCI: mediatek: Clear IRQ status ...

s/dispathed/dispatched/

s/irq/IRQ/ in the summary and all the English text below.

On Wed, Dec 20, 2017 at 10:52:14AM +0800, honghui.zhang at mediatek.com wrote:
> From: Honghui Zhang <honghui.zhang at mediatek.com>
> 
> There maybe a same irq reentry scenario after irq received in current
> irq handle flow:
> 	EP device		PCIe host driver	EP driver
> 1. issue an irq
> 			2. received irq
> 			3. clear irq status
> 			4. dispatch irq
> 						5. clear irq source
> The irq status was not successfully cleared at step 2 since the irq
> source was not cleared yet. So the PCIe host driver may receive the
> same irq after step 5. Then there's an irq reentry occurred.
> Even worse, if the reentry irq was not an irq that EP driver expected,
> it may not handle the irq. Then we may run into the dead loop from

By "dead loop" I assume you mean "infinite loop"?  I don't think it's
a deadlock since nothing is waiting.

> step 2 to step 4.
> Clear the irq status after irq have been dispatched to avoid the irq
> reentry.
> 
> Signed-off-by: Honghui Zhang <honghui.zhang at mediatek.com>
> ---
>  drivers/pci/host/pcie-mediatek.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/host/pcie-mediatek.c b/drivers/pci/host/pcie-mediatek.c
> index db93efd..3248771 100644
> --- a/drivers/pci/host/pcie-mediatek.c
> +++ b/drivers/pci/host/pcie-mediatek.c
> @@ -605,11 +605,11 @@ static irqreturn_t mtk_pcie_intr_handler(int irq, void *data)
>  
>  	while ((status = readl(port->base + PCIE_INT_STATUS)) & INTX_MASK) {
>  		for_each_set_bit_from(bit, &status, PCI_NUM_INTX + INTX_SHIFT) {
> -			/* Clear the INTx */
> -			writel(1 << bit, port->base + PCIE_INT_STATUS);
>  			virq = irq_find_mapping(port->irq_domain,
>  						bit - INTX_SHIFT);
>  			generic_handle_irq(virq);
> +			/* Clear the INTx */
> +			writel(1 << bit, port->base + PCIE_INT_STATUS);
>  		}
>  	}
>  
> @@ -619,10 +619,10 @@ static irqreturn_t mtk_pcie_intr_handler(int irq, void *data)
>  
>  			while ((imsi_status = readl(port->base + PCIE_IMSI_STATUS))) {
>  				for_each_set_bit(bit, &imsi_status, MTK_MSI_IRQS_NUM) {
> -					/* Clear the MSI */
> -					writel(1 << bit, port->base + PCIE_IMSI_STATUS);
>  					virq = irq_find_mapping(port->msi_domain, bit);
>  					generic_handle_irq(virq);
> +					/* Clear the MSI */
> +					writel(1 << bit, port->base + PCIE_IMSI_STATUS);
>  				}
>  			}
>  			/* Clear MSI interrupt status */
> -- 
> 2.6.4
> 
> 
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