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

Kishon Vijay Abraham I
2021-08-09T04:50:30Z

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@ti.com> 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@ti.com>
>> ---
>> 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