linux-kernel - Re: [PATCH v2 00/10] Add support for TISCI irqchip drivers

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Date:   Tue, 23 Oct 2018 10:34:14 -0700
From:   Santosh Shilimkar <santosh.shilimkar@...cle.com>
To:     Lokesh Vutla <lokeshvutla@...com>, Nishanth Menon <nm@...com>,
        Rob Herring <robh+dt@...nel.org>, tglx@...utronix.de,
        jason@...edaemon.net, marc.zyngier@....com
Cc:     Santosh Shilimkar <ssantosh@...nel.org>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, Tero Kristo <t-kristo@...com>,
        Sekhar Nori <nsekhar@...com>,
        Device Tree Mailing List <devicetree@...r.kernel.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Peter Ujfalusi <peter.ujfalusi@...com>
Subject: Re: [PATCH v2 00/10] Add support for TISCI irqchip drivers

On 10/23/2018 1:17 AM, Lokesh Vutla wrote:
> Hi Santosh,
> 
> On Tuesday 23 October 2018 02:09 AM, Santosh Shilimkar wrote:
>> On 10/18/2018 8:40 AM, Lokesh Vutla wrote:
>>> TISCI abstracts the handling of IRQ routes where interrupt sources
>>> are not directly connected to host interrupt controller. This series
>>> adds support for:
>>> - TISCI commands needed for IRQ configuration
>>> - Interrupt Router(INTR) and Interrupt Aggregator(INTA) drivers
>>>
>>> More information on TISCI IRQ management can be found here[1].
>>> Complete TISCI resource management information can be found here[2].
>>> AM65x SoC related TISCI information can be found here[3].
>>> INTR and INTA related information can be found in TRM[4].
>>>
>> I didn't read the specs but from what you described in
>> INTA and INTR bindings, does the flow of IRQs like below ?
>>
>> Device IRQ(e.g USB) -->INTR-->INTA--->HOST IRQ controller(GIC)
> 
> Not all devices in SoC are connected to INTA. Only the devices that are 
> capable of generating events are connected to INTA. And INTA is 
> connected to INTR.
> 
> So there are three ways in which IRQ can flow in AM65x SoC:
> 1) Device directly connected to GIC
>      - Device IRQ --> GIC
>      - (Most legacy peripherals like MMC, UART falls in this case)
> 2) Device connected to INTR.
>      - Device IRQ --> INTR --> GIC
>      - This is cases where you want to mux IRQs. Used for GPIOs and 
> Mailboxes
>      - (This is somewhat similar to crossbar on DRA7 devices)
> 3) Devices connected to INTA.
>      - Device Event --> INTA --> INTR --> GIC
>      - Used for DMA and networking devices.
> 
> Events are messages based on a hw protocol, sent by a master over a 
> dedicated Event transport lane. Events are highly precise that no 
> under/over flow of data transfer occurs at source/destination regardless 
> of distance and latency. So this is mostly preferred in DMA and 
> networking usecases. Now Interrupt Aggregator(IA) has the logic to 
> converts these events to Interrupts.
> 
This helps but none of the kernel doc you added, makes this clear so
perhaps you want to add this info to make that clear for reviewers
as well as for future reference.

Now regarding the events, no matter how they are routed/processed
within SOC, they are essentially interrupts so I do agree with
Marc's other comment.

Thanks for explanation again !!

regards,
Santosh