linux-kernel - Re: [PATCH 5/6] PCI: keystone: Add PCI legacy interrupt support for AM654

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Date:   Fri, 02 Apr 2021 12:11:24 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Lokesh Vutla <lokeshvutla@...com>
Subject: Re: [PATCH 5/6] PCI: keystone: Add PCI legacy interrupt support for AM654

On Thu, 25 Mar 2021 09:00:25 +0000,
Kishon Vijay Abraham I <kishon@...com> wrote:
> 
> Add PCI legacy interrupt support for AM654. AM654 has a single HW
> interrupt line for all the four legacy interrupts INTA/INTB/INTC/INTD.
> The HW interrupt line connected to GIC is a pulse interrupt whereas
> the legacy interrupts by definition is level interrupt. In order to
> provide level interrupt functionality to edge interrupt line, PCIe
> in AM654 has provided IRQ_EOI register. When the SW writes to IRQ_EOI
> register after handling the interrupt, the IP checks the state of
> legacy interrupt and re-triggers pulse interrupt invoking the handler
> again.
> 
> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
> ---
>  drivers/pci/controller/dwc/pci-keystone.c | 87 +++++++++++++++++++++--
>  1 file changed, 82 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-keystone.c b/drivers/pci/controller/dwc/pci-keystone.c
> index dfa9a7fcf9b7..84a25207d0d3 100644
> --- a/drivers/pci/controller/dwc/pci-keystone.c
> +++ b/drivers/pci/controller/dwc/pci-keystone.c
> @@ -118,6 +118,7 @@ struct keystone_pcie {
>  	/* PCI Device ID */
>  	u32			device_id;
>  	struct			device_node *legacy_intc_np;
> +	struct irq_domain	*legacy_irq_domain;
>  
>  	int			msi_host_irq;
>  	int			num_lanes;
> @@ -289,6 +290,29 @@ static irqreturn_t ks_pcie_handle_error_irq(struct keystone_pcie *ks_pcie)
>  	return IRQ_HANDLED;
>  }
>  
> +static void ks_pcie_am654_legacy_irq_handler(struct irq_desc *desc)
> +{
> +	struct keystone_pcie *ks_pcie = irq_desc_get_handler_data(desc);
> +	struct irq_chip *chip = irq_desc_get_chip(desc);
> +	int virq, i;
> +	u32 reg;
> +
> +	chained_irq_enter(chip, desc);
> +
> +	for (i = 0; i < PCI_NUM_INTX; i++) {
> +		reg = ks_pcie_app_readl(ks_pcie, IRQ_STATUS(i));
> +		if (!(reg & INTx_EN))
> +			continue;
> +
> +		virq = irq_linear_revmap(ks_pcie->legacy_irq_domain, i);
> +		generic_handle_irq(virq);

I'm on my way to kill irq_linear_revmap(), so I'd rather you didn't
add more instances. Consider using irq_find_mapping() instead.

> +		ks_pcie_app_writel(ks_pcie, IRQ_STATUS(i), INTx_EN);
> +		ks_pcie_app_writel(ks_pcie, IRQ_EOI, i);

What are these writes for? The first one feels like an Ack, and the
second one has EOI written over it.

If that's what they are, llease move these to a proper irq_chip
structure and use the appropriate flow handler, instead of
dummy_irq_chip and handle_simple_irq.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.