Re: [PATCH 1/1] PCI: dwc: Use regular interrupt instead of chained

[Bjorn Helgaas]

On Thu, Jun 29, 2023 at 02:30:19PM -0400, Radu Rendec wrote:
> The DesignWare PCIe host driver uses a chained interrupt to demultiplex
> the downstream MSI interrupts. On Qualcomm SA8540P Ride, enabling both
> pcie2a and pcie3a at the same time can create an interrupt storm where
> the parent interrupt fires continuously, even though reading the PCIe
> host registers doesn't identify any child MSI interrupt source. This
> effectively locks up CPU0, which spends all the time servicing these
> interrupts.
> 
> This is a clear example of how bypassing the interrupt core by using
> chained interrupts can be very dangerous if the hardware misbehaves.
> 
> Convert the driver to use a regular interrupt for the demultiplex
> handler. This allows the interrupt storm detector to detect the faulty
> interrupt and disable it, allowing the system to run normally.

There are many other users of irq_set_chained_handler_and_data() in
drivers/pci/controller/.  Should they be similarly converted?  If not,
how do we decide which need to use irq_set_chained_handler_and_data()
and which do not?

> Signed-off-by: Radu Rendec <rrendec@xxxxxxxxxx>
> ---
>  .../pci/controller/dwc/pcie-designware-host.c | 35 +++++++++----------
>  1 file changed, 17 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 9952057c8819c..b603796d415d7 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -83,18 +83,9 @@ irqreturn_t dw_handle_msi_irq(struct dw_pcie_rp *pp)
>  	return ret;
>  }
>  
> -/* Chained MSI interrupt service routine */
> -static void dw_chained_msi_isr(struct irq_desc *desc)
> +static irqreturn_t dw_pcie_msi_isr(int irq, void *dev_id)
>  {
> -	struct irq_chip *chip = irq_desc_get_chip(desc);
> -	struct dw_pcie_rp *pp;
> -
> -	chained_irq_enter(chip, desc);
> -
> -	pp = irq_desc_get_handler_data(desc);
> -	dw_handle_msi_irq(pp);
> -
> -	chained_irq_exit(chip, desc);
> +	return dw_handle_msi_irq(dev_id);
>  }
>  
>  static void dw_pci_setup_msi_msg(struct irq_data *d, struct msi_msg *msg)
> @@ -254,20 +245,21 @@ int dw_pcie_allocate_domains(struct dw_pcie_rp *pp)
>  	return 0;
>  }
>  
> -static void dw_pcie_free_msi(struct dw_pcie_rp *pp)
> +static void __dw_pcie_free_msi(struct dw_pcie_rp *pp, u32 num_ctrls)
>  {
>  	u32 ctrl;
>  
> -	for (ctrl = 0; ctrl < MAX_MSI_CTRLS; ctrl++) {
> +	for (ctrl = 0; ctrl < num_ctrls; ctrl++) {
>  		if (pp->msi_irq[ctrl] > 0)
> -			irq_set_chained_handler_and_data(pp->msi_irq[ctrl],
> -							 NULL, NULL);
> +			free_irq(pp->msi_irq[ctrl], pp);
>  	}
>  
>  	irq_domain_remove(pp->msi_domain);
>  	irq_domain_remove(pp->irq_domain);
>  }
>  
> +#define dw_pcie_free_msi(pp) __dw_pcie_free_msi(pp, MAX_MSI_CTRLS)

What is the benefit of the dw_pcie_free_msi() macro?

>  static void dw_pcie_msi_init(struct dw_pcie_rp *pp)
>  {
>  	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> @@ -361,9 +353,16 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
>  		return ret;
>  
>  	for (ctrl = 0; ctrl < num_ctrls; ctrl++) {
> -		if (pp->msi_irq[ctrl] > 0)
> -			irq_set_chained_handler_and_data(pp->msi_irq[ctrl],
> -						    dw_chained_msi_isr, pp);
> +		if (pp->msi_irq[ctrl] > 0) {
> +			ret = request_irq(pp->msi_irq[ctrl], dw_pcie_msi_isr, 0,
> +					  dev_name(dev), pp);
> +			if (ret) {
> +				dev_err(dev, "Failed to request irq %d: %d\n",
> +					pp->msi_irq[ctrl], ret);
> +				__dw_pcie_free_msi(pp, ctrl);
> +				return ret;
> +			}
> +		}
>  	}
>  
>  	/*
> -- 
> 2.41.0
>