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

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Date:   Mon, 12 Oct 2020 08:31:45 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     nm@...com, devicetree@...r.kernel.org, jason@...edaemon.net,
        lokeshvutla@...com, linux-kernel@...r.kernel.org, t-kristo@...com,
        robh+dt@...nel.org, ssantosh@...nel.org, tglx@...utronix.de,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] irqchip/ti-sci-inta: Add support for unmapped
 event handling

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.

         M.
-- 
Jazz is not dead. It just smells funny...