Re: [PATCH v2 09/10] irqchip: ti-sci-inta: Add support for Interrupt Aggregator driver

From: Lokesh Vutla
Date: Fri Oct 26 2018 - 16:20:40 EST

Hi Marc,


+ * ti_sci_inta_register_event() - Register a event to an interrupt aggregator
+ * @dev: Device pointer to source generating the event
+ * @src_id: TISCI device ID of the event source
+ * @src_index: Event source index within the device.
+ * @virq: Linux Virtual IRQ number
+ * @flags: Corresponding IRQ flags
+ * @ack_needed: If explicit clearing of event is required.
+ *
+ * Creates a new irq and attaches to IA domain if virq is not specified
+ * else attaches the event to vint corresponding to virq.
+ * When using TISCI within the client drivers, source indexes are always
+ * generated dynamically and cannot be represented in DT. So client
+ * drivers should call this API instead of platform_get_irq().

NAK. Either this fits in the standard model, or we adapt the standard
model to catter for your particular use case. But we don't define a new,
TI specific API.

I have a hunch that if the IDs are generated dynamically, then the model
we use for MSIs would fit this thing. I also want to understand what

hmm..I haven't thought about using MSI. Will try to explore it. But
the "struct msi_msg" is not applicable in this case as device does not
write to a specific location.

It doesn't need to. You can perfectly ignore the address field and
only be concerned with the data. We already have MSI users that do not
need programming of the doorbell address, just the data.

Just one more clarification.

First let me explain the IRQ routes a bit deeply. As I said earlier there are three ways in which IRQ can flow in AM65x SoC
1) Device directly connected to GIC
- Device IRQ --> GIC
2) Device connected to INTR.
- Device IRQ --> INTR --> GIC
3) Devices connected to INTA.
- Device IRQ --> INTA --> INTR --> GIC

1 and 2 are straight forward and we use DT for IRQ representation. Coming to 3 the trickier part is that Input to INTA and output from INTA and dynamically managed. To be more specific:
- By hardware design there are certain set of physical global events(interrupts) attached to an INTA. Out of which a certain range are assigned to the current linux host that can be queried from system-controller.
- Similarly out of all the INTA outputs(referenced as vints) a certain range can be used by the current linux host.

So for configuring an IRQ route in case 3, the following steps are needed:
- Device id and device resource index for which the interrupt is needed
- A free event id from the range assigned to the INTA in this host context
- A free vint from the range assigned to the INTA in this host context
- A free gic IRQ from the range assigned to the INTR in this host context.

With the above information, linux should send a message to system-controller using TISCI protocol. After policing the given information, system-controller does the following:
- Attaches the interrupt(INTA input) to the device resource index
- Muxes the interrupt(INTA input) to corresponding vint(INTA output)
- Muxes the vint(INTR input) to GIC irq(INTR output).

For grouping of interrupts, the same vint number is to be passed to system-controller for all the requests.

Keeping all the above in mind, I see the following as software IRQ Domain Hierarchy:

1) INTA multi MSI --> 2)INTA -->3) MSI --> 4) INTR -->5) GIC

INTA driver has to set a chained IRQ using virq allocated from its parent MSI. This is to differentiate the grouped interrupts within INTA.

Inorder to cover the above two MSI domains, a new bus driver has to be created as I couldn't find a fit with the existing bus drivers.

Does the above approach make sense? Please correct me if i am wrong.

Thanks and regards,