Re: [PATCH v2 2/3] PCI: j721e: Add PCI legacy interrupt support for J721E

[Kishon Vijay Abraham I]

Hi Marc,

On 04/08/21 8:43 pm, Marc Zyngier wrote:
> On Wed, 04 Aug 2021 14:29:11 +0100,
> Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
>>
>> Add PCI legacy interrupt support for J721E. J721E 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 J721E has provided IRQ_EOI register.
>>
>> However due to Errata ID #i2094 ([1]), EOI feature is not enabled in HW
>> and only a single pulse interrupt will be generated for every
>> ASSERT_INTx/DEASSERT_INTx.
> 
> So my earlier remark stands. If you get a single edge, how do you
> handle a level that is still high after having handled the interrupt
> on hardware that has this bug?

Right, this hardware (J721E) has a bug but was fixed in J7200 (Patch 3/3
handles that).
> 
>>
>> [1] -> J721E DRA829/TDA4VM Processors Silicon Revision 1.1/1.0 SPRZ455A –
>>        DECEMBER 2020 – REVISED AUGUST 2021
>>        (https://www.ti.com/lit/er/sprz455a/sprz455a.pdf)
>>
>> Signed-off-by: Kishon Vijay Abraham I <kishon@xxxxxx>
>> ---
>>  drivers/pci/controller/cadence/pci-j721e.c | 85 ++++++++++++++++++++++
>>  1 file changed, 85 insertions(+)
>>
>> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
>> index 2ec037c43bd5..c2e7a78dc31f 100644
>> --- a/drivers/pci/controller/cadence/pci-j721e.c
>> +++ b/drivers/pci/controller/cadence/pci-j721e.c
>> @@ -29,6 +29,13 @@
>>  #define LINK_DOWN		BIT(1)
>>  #define J7200_LINK_DOWN		BIT(10)
>>  
>> +#define EOI_REG			0x10
>> +
>> +#define ENABLE_REG_SYS_0	0x100
>> +#define STATUS_REG_SYS_0	0x500
>> +#define STATUS_CLR_REG_SYS_0	0x700
>> +#define INTx_EN(num)		(1 << (num))
>> +
>>  #define J721E_PCIE_USER_CMD_STATUS	0x4
>>  #define LINK_TRAINING_ENABLE		BIT(0)
>>  
>> @@ -59,6 +66,7 @@ struct j721e_pcie {
>>  	void __iomem		*user_cfg_base;
>>  	void __iomem		*intd_cfg_base;
>>  	u32			linkdown_irq_regfield;
>> +	struct irq_domain	*legacy_irq_domain;
>>  };
>>  
>>  enum j721e_pcie_mode {
>> @@ -121,6 +129,79 @@ static void j721e_pcie_config_link_irq(struct j721e_pcie *pcie)
>>  	j721e_pcie_intd_writel(pcie, ENABLE_REG_SYS_2, reg);
>>  }
>>  
>> +static void j721e_pcie_v1_legacy_irq_handler(struct irq_desc *desc)
>> +{
>> +	struct j721e_pcie *pcie = irq_desc_get_handler_data(desc);
>> +	struct irq_chip *chip = irq_desc_get_chip(desc);
>> +	int i, virq;
>> +	u32 reg;
>> +
>> +	chained_irq_enter(chip, desc);
>> +
>> +	for (i = 0; i < PCI_NUM_INTX; i++) {
>> +		reg = j721e_pcie_intd_readl(pcie, STATUS_REG_SYS_0);
>> +		if (!(reg & INTx_EN(i)))
>> +			continue;
> 
> Why do you need to perform multiple reads? Surely reg contains all the
> bits you need, doesn't it?

Right, will fix it up.
> 
>> +
>> +		virq = irq_find_mapping(pcie->legacy_irq_domain, 3 - i);
>> +		generic_handle_irq(virq);
> 
> Please combine both lines into a single generic_handle_domain_irq()
> call.

Okay.
> 
>> +		j721e_pcie_intd_writel(pcie, STATUS_CLR_REG_SYS_0, INTx_EN(i));
> 
> What is the purpose of this write? It feels like this should be a
> irq_eoi callback.

It's an IRQ ACK, since in this platform the level to edge is not
implemented properly in HW.
> 
>> +	}
>> +
>> +	chained_irq_exit(chip, desc);
>> +}
>> +
>> +static int j721e_pcie_intx_map(struct irq_domain *domain, unsigned int irq, irq_hw_number_t hwirq)
>> +{
>> +	irq_set_chip_and_handler(irq, &dummy_irq_chip, handle_simple_irq);
> 
> An INTx interrupt is a level interrupt. Please use the corresponding flow.

Okay.
> 
>> +	irq_set_chip_data(irq, domain->host_data);
>> +
>> +	return 0;
>> +}
>> +
>> +static const struct irq_domain_ops j721e_pcie_intx_domain_ops = {
>> +	.map = j721e_pcie_intx_map,
>> +};
>> +
>> +static int j721e_pcie_config_legacy_irq(struct j721e_pcie *pcie)
>> +{
>> +	struct irq_domain *legacy_irq_domain;
>> +	struct device *dev = pcie->dev;
>> +	struct device_node *node = dev->of_node;
>> +	struct device_node *intc_node;
>> +	int irq, i;
>> +	u32 reg;
>> +
>> +	intc_node = of_get_child_by_name(node, "interrupt-controller");
>> +	if (!intc_node) {
>> +		dev_dbg(dev, "interrupt-controller node is absent. Legacy INTR not supported\n");
>> +		return 0;
>> +	}
>> +
>> +	irq = irq_of_parse_and_map(intc_node, 0);
>> +	if (!irq) {
>> +		dev_err(dev, "Failed to parse and map legacy irq\n");
>> +		return -EINVAL;
>> +	}
>> +	irq_set_chained_handler_and_data(irq, j721e_pcie_v1_legacy_irq_handler, pcie);
>> +
>> +	legacy_irq_domain = irq_domain_add_linear(intc_node, PCI_NUM_INTX,
>> +						  &j721e_pcie_intx_domain_ops, pcie);
>> +	if (!legacy_irq_domain) {
>> +		dev_err(dev, "Failed to add irq domain for legacy irqs\n");
>> +		return -EINVAL;
>> +	}
>> +	pcie->legacy_irq_domain = legacy_irq_domain;
>> +
>> +	for (i = 0; i < PCI_NUM_INTX; i++) {
>> +		reg = j721e_pcie_intd_readl(pcie, ENABLE_REG_SYS_0);
>> +		reg |= INTx_EN(i);
>> +		j721e_pcie_intd_writel(pcie, ENABLE_REG_SYS_0, reg);
>> +	}
> 
> This should be moved to the irq_unmask() callback.

Should we also have a corresponding irq_mask()? Then would require us
implement reference counting since legacy interrupts are shared.

Thanks,
Kishon