Re: [PATCH v2] PCI/DPC: Fix shared interrupt handling

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Dec 14, 2017 at 08:20:18AM -0700, Alex Williamson wrote:
> DPC supports shared interrupts, but it plays very loosely with testing
> whether the interrupt is generated by DPC before generating spurious
> log messages, such as:
> 
>  dpc 0000:10:01.2:pcie010: DPC containment event, status:0x1f00 source:0x0000
> 
> Testing the status register for zero or -1 is not sufficient when the
> device supports the RP PIO First Error Pointer register.  Change this
> to test whether the interrupt is enabled in the control register,
> retaining the device present test, and that the status reports the
> interrupt as signaled and DPC is triggered, clearing as a spurious
> interrupt otherwise.
> 
> Additionally, since the interrupt is actually serviced by a workqueue,
> disable the interrupt in the control register until that completes or
> else we may never see it execute due to further incoming interrupts.
> A software generated DPC floods the system otherwise.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Applied with Keith's reviewed-by on pci/dpc for v4.16, thanks!

> ---
> 
> v2: Fix interrupt re-enable as spotted by Keith, tested multiple
>     injections via software trigger.
> 
>  drivers/pci/pcie/pcie-dpc.c |   60 +++++++++++++++++++++++++++++--------------
>  1 file changed, 40 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/pci/pcie/pcie-dpc.c b/drivers/pci/pcie/pcie-dpc.c
> index 2d976a623ddc..f7cf5ae7dec2 100644
> --- a/drivers/pci/pcie/pcie-dpc.c
> +++ b/drivers/pci/pcie/pcie-dpc.c
> @@ -109,6 +109,7 @@ static void interrupt_event_handler(struct work_struct *work)
>  	struct dpc_dev *dpc = container_of(work, struct dpc_dev, work);
>  	struct pci_dev *dev, *temp, *pdev = dpc->dev->port;
>  	struct pci_bus *parent = pdev->subordinate;
> +	u16 ctl;
>  
>  	pci_lock_rescan_remove();
>  	list_for_each_entry_safe_reverse(dev, temp, &parent->devices,
> @@ -135,6 +136,10 @@ static void interrupt_event_handler(struct work_struct *work)
>  
>  	pci_write_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_STATUS,
>  		PCI_EXP_DPC_STATUS_TRIGGER | PCI_EXP_DPC_STATUS_INTERRUPT);
> +
> +	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CTL, &ctl);
> +	pci_write_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CTL,
> +			      ctl | PCI_EXP_DPC_CTL_INT_EN);
>  }
>  
>  static void dpc_rp_pio_print_tlp_header(struct device *dev,
> @@ -249,34 +254,49 @@ static irqreturn_t dpc_irq(int irq, void *context)
>  	struct dpc_dev *dpc = (struct dpc_dev *)context;
>  	struct pci_dev *pdev = dpc->dev->port;
>  	struct device *dev = &dpc->dev->device;
> -	u16 status, source;
> +	u16 ctl, status, source, reason, ext_reason;
> +
> +	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CTL, &ctl);
> +
> +	if (!(ctl & PCI_EXP_DPC_CTL_INT_EN) || ctl == (u16)(~0))
> +		return IRQ_NONE;
>  
>  	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_STATUS, &status);
> +
> +	if (!(status & PCI_EXP_DPC_STATUS_INTERRUPT))
> +		return IRQ_NONE;
> +
> +	if (!(status & PCI_EXP_DPC_STATUS_TRIGGER)) {
> +		pci_write_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_STATUS,
> +				      PCI_EXP_DPC_STATUS_INTERRUPT);
> +		return IRQ_HANDLED;
> +	}
> +
> +	pci_write_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CTL,
> +			      ctl & ~PCI_EXP_DPC_CTL_INT_EN);
> +
>  	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_SOURCE_ID,
>  			     &source);
> -	if (!status || status == (u16)(~0))
> -		return IRQ_NONE;
>  
>  	dev_info(dev, "DPC containment event, status:%#06x source:%#06x\n",
>  		status, source);
>  
> -	if (status & PCI_EXP_DPC_STATUS_TRIGGER) {
> -		u16 reason = (status >> 1) & 0x3;
> -		u16 ext_reason = (status >> 5) & 0x3;
> -
> -		dev_warn(dev, "DPC %s detected, remove downstream devices\n",
> -			 (reason == 0) ? "unmasked uncorrectable error" :
> -			 (reason == 1) ? "ERR_NONFATAL" :
> -			 (reason == 2) ? "ERR_FATAL" :
> -			 (ext_reason == 0) ? "RP PIO error" :
> -			 (ext_reason == 1) ? "software trigger" :
> -					     "reserved error");
> -		/* show RP PIO error detail information */
> -		if (reason == 3 && ext_reason == 0)
> -			dpc_process_rp_pio_error(dpc);
> -
> -		schedule_work(&dpc->work);
> -	}
> +	reason = (status >> 1) & 0x3;
> +	ext_reason = (status >> 5) & 0x3;
> +
> +	dev_warn(dev, "DPC %s detected, remove downstream devices\n",
> +		 (reason == 0) ? "unmasked uncorrectable error" :
> +		 (reason == 1) ? "ERR_NONFATAL" :
> +		 (reason == 2) ? "ERR_FATAL" :
> +		 (ext_reason == 0) ? "RP PIO error" :
> +		 (ext_reason == 1) ? "software trigger" :
> +				     "reserved error");
> +	/* show RP PIO error detail information */
> +	if (reason == 3 && ext_reason == 0)
> +		dpc_process_rp_pio_error(dpc);
> +
> +	schedule_work(&dpc->work);
> +
>  	return IRQ_HANDLED;
>  }
>  
>