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SubjectRe: [Patch net-next v4 05/13] net: dsa: microchip: ptp: enable interrupt for timestamping
On Mon, Dec 12, 2022 at 03:56:31PM +0530, Arun Ramadoss wrote:
> +int ksz_ptp_irq_setup(struct dsa_switch *ds, u8 p)
> +{
> + struct ksz_device *dev = ds->priv;
> + const struct ksz_dev_ops *ops = dev->dev_ops;
> + struct ksz_port *port = &dev->ports[p];
> + struct ksz_irq *ptpirq = &port->ptpirq;
> + int ret;
> +
> + ptpirq->dev = dev;
> + ptpirq->masked = 0;
> + ptpirq->nirqs = 3;
> + ptpirq->reg_mask = ops->get_port_addr(p, REG_PTP_PORT_TX_INT_ENABLE__2);
> + ptpirq->reg_status = ops->get_port_addr(p,
> + REG_PTP_PORT_TX_INT_STATUS__2);
> + snprintf(ptpirq->name, sizeof(ptpirq->name), "ptp_irq-%d", p);
> +
> + ptpirq->irq_num = irq_find_mapping(port->pirq.domain, PORT_SRC_PTP_INT);
> + if (ptpirq->irq_num < 0)
> + return ptpirq->irq_num;
> +
> + ptpirq->domain = irq_domain_add_simple(dev->dev->of_node, ptpirq->nirqs,
> + 0, &ksz_ptp_irq_domain_ops,
> + ptpirq);

If I look at Documentation/core-api/irq/irq-domain.rst, I read this:

| Legacy
| ------
|
| ::
|
| irq_domain_add_simple()
| irq_domain_add_legacy()
| irq_domain_create_simple()
| irq_domain_create_legacy()
|
| The Legacy mapping is a special case for drivers that already have a
| range of irq_descs allocated for the hwirqs. It is used when the
| driver cannot be immediately converted to use the linear mapping. For
| example, many embedded system board support files use a set of #defines
| for IRQ numbers that are passed to struct device registrations. In that
| case the Linux IRQ numbers cannot be dynamically assigned and the legacy
| mapping should be used.
|
| As the name implies, the \*_legacy() functions are deprecated and only
| exist to ease the support of ancient platforms. No new users should be
| added. Same goes for the \*_simple() functions when their use results
| in the legacy behaviour.
|
| The legacy map assumes a contiguous range of IRQ numbers has already
| been allocated for the controller and that the IRQ number can be
| calculated by adding a fixed offset to the hwirq number, and
| visa-versa. The disadvantage is that it requires the interrupt
| controller to manage IRQ allocations and it requires an irq_desc to be
| allocated for every hwirq, even if it is unused.
|
| The legacy map should only be used if fixed IRQ mappings must be
| supported. For example, ISA controllers would use the legacy map for
| mapping Linux IRQs 0-15 so that existing ISA drivers get the correct IRQ
| numbers.
|
| Most users of legacy mappings should use irq_domain_add_simple() or
| irq_domain_create_simple() which will use a legacy domain only if an IRQ range
| is supplied by the system and will otherwise use a linear domain mapping.
| The semantics of this call are such that if an IRQ range is specified then
| descriptors will be allocated on-the-fly for it, and if no range is
| specified it will fall through to irq_domain_add_linear() or
| irq_domain_create_linear() which means *no* irq descriptors will be allocated.

I think you should be absolutely fine with using irq_domain_add_linear().

> + if (!ptpirq->domain)
> + return -ENOMEM;
> +
> + ret = request_threaded_irq(ptpirq->irq_num, NULL, ksz_ptp_irq_thread_fn,
> + IRQF_ONESHOT, ptpirq->name, ptpirq);
> + if (ret)
> + goto out;
> +
> + ret = ksz_ptp_msg_irq_setup(port);
> + if (ret)
> + goto out;

I think the error path is a bit shaky. Since request_threaded_irq() is
not the devres variant (devm_request_threaded_irq()), there should be a
free_irq() call on error.

> +
> + return 0;
> +
> +out:
> + irq_dispose_mapping(ptpirq->irq_num);
> +
> + return ret;
> +}

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