Re: [PATCH v2 2/2] irqchip/ti-sci-inta: Add support for unmapped event handling

[Peter Ujfalusi]

On 12/10/2020 10.31, Marc Zyngier wrote:
> On 2020-10-09 09:58, Peter Ujfalusi wrote:
>> Marc,
>>
> 
> [...]
> 
>> The design of irqchip/irq-ti-sci-inta.c, soc/ti/ti_sci_inta_msi.c and
>> irqchip/irq-ti-sci-intr.c created to handle the interrupt needs present
>> in K3 devices with NAVSS.
>> DMSS of newer K3 devices extends and simplifies the NAVSS components and
>> a big part of that change was done with the INTA and DMAs.
>> System Firmware also changed to adopt to these changes.
>>
>> As an example, let's assume that we want an interrupt from a ring.
>> The high level of the events in this case are:
>>
>> NAVSS:
>> 1.1 ring generates an internal signal (up or down)
>> 1.2 the ringacc will send a (mapped) Global Event to INTA
>> 1.3 When INTA receives the global event, it will signal it's outgoing
>>     VINT to INTR
>> 1.4 INTR will trigger a host interrupt.
>>
>> DMSS
>> 1.1 ring generates an internal signal (up or down)
>> 1.2 the DMA (ring is now part of the DMA) will send an unmapped event to
>>     INTA
>> 1.3 When INTA receives the unmapped event, it will send a (mapped)
>>     Global Event to itself
>> 1.4 When INTA receives the global event, it will signal it's outgoing
>>     VINT to INTR
>> 1.5 INTR will trigger a host interrupt.
>>
>> The API from sysfw is the same to configure the global events and VINT,
>> but we need to use the INTA's tisci device identification number to let
>> sysfw know that the Global event number can be programmed into INTA's
>> unmapped event steering register. The DMA no longer have this register,
>> it sends unmapped event to INTA.
>>
>> The unmapped event number is fixed per sources, they will arrive at the
>> specific unmapped event configuration register of INTA.
>>
>> INTA itself does not know which source are allocated to be used by
>> Linux, the allocation is for the DMA resources and only the DMA driver
>> knows which channels, rings, flows can be used and can ask the INTA MSI
>> domain to create interrupts for those.
>>
>> By handling the ti,unmapped-event-sources the INTA driver can make
>> decision on the correct tisci dev_id to be used for the sysfw API to
>> where the global event must be configured and the client drivers does
>> not need to know how things are working under the hood.
>>
>> There are components in DMSS which use is exactly how they worked within
>> NAVSS, they are not using unmapped events. Ringacc comes to mind first.
>>
>> I can add a comment block to explain the nature of unmapped events and
>> the reason why we need to do what we do.
>>
>> Would this be acceptable?
> 
> That'd be useful, as long as it is shorter than the above.

OK, I will send an update next week after I'm back.


- Péter

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