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

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Message-ID: <bc7312c2-b068-ddda-b183-54e6bc3f8219@ti.com>
Date:   Fri, 26 Oct 2018 12:09:01 +0530
From:   Lokesh Vutla <lokeshvutla@...com>
To:     Santosh Shilimkar <santosh.shilimkar@...cle.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

Hi Santosh,

On Tuesday 23 October 2018 11:04 PM, Santosh Shilimkar wrote:
> 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.

Sure will add it.

> 
> 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.

Agreed. Marc suggested to use MSI in this scenario. Currently working in that 
direction. Will repost the series once it is done.

Thanks and regards,
Lokesh

> 
> Thanks for explanation again !!
> 
> regards,
> Santosh
>