Subject: Re: [PATCH v2 2/9] PCI: keystone: Modify legacy_irq_handler to check the IRQ_STATUS of INTA/B/C/D

From: Bjorn Helgaas <[email-masked]>
Date: Thu, 7 Feb 2019 14:52:57 -0600

In the subject, "legacy_irq_handler" looks like it's supposed to be a
function name, but it's not.  Maybe something like:

  PCI: keystone: Check INTA/B/C/D IRQ_STATUS in ks_pcie_legacy_irq_handler()

On Thu, Feb 07, 2019 at 04:39:17PM +0530, Kishon Vijay Abraham I wrote:
> The legacy interrupt handler directly checks the IRQ_STATUS register
> corresponding to a interrupt line inorder to invoke generic_handle_irq.

s/The legacy interrupt handler/ks_pcie_handle_legacy_irq()/ ?
s/to a/to an/
s/inorder/in order/
s/generic_handle_irq/generic_handle_irq()/

> While this is okay for K2G platform which has separate interrupt line for
> each of the 4 legacy interrupts, AM654 which uses the same PCIe wrapper
> has a single interrupt line for all the legacy interrupts. So for AM654
> the interrupt handler won't be able to directly check the IRQ_STATUS
> register corresponding to the interrupt line.

s/platform which/platform, which/
s/separate interrupt line/separate interrupt lines/
s/AM654 which/AM654, which/
s/PCIe wrapper/PCIe wrapper,/
s/interrupt line for all/interrupt line shared by all/

> Also the legacy interrupt handler uses 'virq' obtained from
> irq_of_parse_and_map to find the correct interrupt line which raised the
> interrupt. There is no guarantee that virq assigned for contiguous hardware
> irq will be contiguous and the interrupt handler might end up checking
> the wrong IRQ_STATUS register.

s/irq_of_parse_and_map/irq_of_parse_and_map()
s/irq will/IRQ will/

> In order to overcome the above issues, read the IRQ_STATUS register of
> all the 4 legacy interrupts to determine which interrupt was raised.
> 
> Link: https://lkml.kernel.org/r/[email-masked]
> Signed-off-by: Kishon Vijay Abraham I <[email-masked]>
> ---
>  drivers/pci/controller/dwc/pci-keystone.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-keystone.c b/drivers/pci/controller/dwc/pci-keystone.c
> index 5286a480f76b..4cf9849d5a1d 100644
> --- a/drivers/pci/controller/dwc/pci-keystone.c
> +++ b/drivers/pci/controller/dwc/pci-keystone.c
> @@ -214,16 +214,11 @@ static void ks_pcie_handle_legacy_irq(struct keystone_pcie *ks_pcie,
>  {
>  	struct dw_pcie *pci = ks_pcie->pci;
>  	struct device *dev = pci->dev;
> -	u32 pending;
>  	int virq;
>  
> -	pending = ks_pcie_app_readl(ks_pcie, IRQ_STATUS(offset));
> -
> -	if (BIT(0) & pending) {
> -		virq = irq_linear_revmap(ks_pcie->legacy_irq_domain, offset);
> -		dev_dbg(dev, ": irq: irq_offset %d, virq %d\n", offset, virq);
> -		generic_handle_irq(virq);
> -	}
> +	virq = irq_linear_revmap(ks_pcie->legacy_irq_domain, offset);
> +	dev_dbg(dev, ": irq: irq_offset %d, virq %d\n", offset, virq);
> +	generic_handle_irq(virq);
>  
>  	/* EOI the INTx interrupt */
>  	ks_pcie_app_writel(ks_pcie, IRQ_EOI, offset);
> @@ -607,8 +602,9 @@ static void ks_pcie_legacy_irq_handler(struct irq_desc *desc)
>  	struct keystone_pcie *ks_pcie = irq_desc_get_handler_data(desc);
>  	struct dw_pcie *pci = ks_pcie->pci;
>  	struct device *dev = pci->dev;
> -	u32 irq_offset = irq - ks_pcie->legacy_host_irqs[0];
>  	struct irq_chip *chip = irq_desc_get_chip(desc);
> +	unsigned int irq_no;
> +	u32 reg;
>  
>  	dev_dbg(dev, ": Handling legacy irq %d\n", irq);
>  
> @@ -618,7 +614,13 @@ static void ks_pcie_legacy_irq_handler(struct irq_desc *desc)
>  	 * ack operation.
>  	 */
>  	chained_irq_enter(chip, desc);
> -	ks_pcie_handle_legacy_irq(ks_pcie, irq_offset);
> +	for (irq_no = 0; irq_no < PCI_NUM_INTX; irq_no++) {
> +		reg = ks_pcie_app_readl(ks_pcie, IRQ_STATUS(irq_no));
> +		if (!(reg & INTx_EN))
> +			continue;
> +		ks_pcie_handle_legacy_irq(ks_pcie, irq_no);

It's too bad that reading IRQ_STATUS and writing IRQ_EOI are now in
separate functions.  It's nice to have them together for code auditing
purposes.

Could maybe accumulate a mask of which INTx bits are set and call
ks_pcie_handle_legacy_irq() only once with that mask?  Of course, then
you'd need another loop in ks_pcie_handle_legacy_irq().

> +	}
> +
>  	chained_irq_exit(chip, desc);
>  }
>  
> -- 
> 2.17.1
> 

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