linux-kernel - Re: [PATCH RFC 0/4] irqchip: qcom: add support for PDC interrupt controller

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Date:   Thu, 25 Jan 2018 15:54:28 +0000
From:   Lina Iyer <ilina@...eaurora.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org, Stephen Boyd <sboyd@...eaurora.org>,
        "Nayak, Rajendra" <rnayak@...eaurora.org>, asathyak@...eaurora.org
Subject: Re: [PATCH RFC 0/4] irqchip: qcom: add support for PDC interrupt
 controller

On Wed, Jan 24 2018 at 17:54 +0000, Sudeep Holla wrote:
>
>
>On 24/01/18 17:43, Lina Iyer wrote:
>> On Wed, Jan 24 2018 at 10:10 +0000, Sudeep Holla wrote:
>>>
>>>
>>> On 23/01/18 18:44, Lina Iyer wrote:
>>>> On Tue, Jan 23 2018 at 18:15 +0000, Sudeep Holla wrote:

>>> Also when will this PDC wakeup interrupts get configured ?
>>>
>> The platform drivers configure the IRQ as a wake source and if the IRQ
>> is one of those listed as routed to the PDC, the PDC is configured to
>> sense the interrupt and when the application processor domain is powered
>> on and the GIC can sense the interrupts, it is replayed to the GIC,
>> which then wakes up the processor.
>>
>
>Now why can't this be done in the firmware entirely, if it can
>save/restore GIC state.
>
That is because platform drivers make the choice of which interrupts are
wake up capable at runtime, based on the usecase. They have to have a
way to tell the firmware to do that. Earlier we used IPC to tell the
remote processor to handle that. Now we do that by writing to the
registers locally from Linux.

>>> OK, understood. By transparent, I mean firmware can copy the interrupts
>>> enabled in the GIC to the PDC. It need not be kernel driven.
>>>
>> Yes, through the hierarchy.
>>
>
>/me confused. Are you saying it's possible for f/w to copy wakeup
>sources from GIC to PDC or not ?
>
Platform drivers leave their interrupts enabled at the GIC. Only
interrupts that are wakeup capable are of interest when the processor is
powered down. The remote processor (or f/w) will need to know the set of
wakeup capable interrupts and then configure the PDC by copying from
GIC. As mentioned earlier, it is simplified by letting Linux write to
the PDC reqisters directly.

>> Yes. There is a partition and protected. So only permitted ELs can write
>> to the registers. This is done by the firmware at boot.
>>
>
>Just for myself to understand better, so you have multiple partitions in
>PDC and one of them is given to EL1 or it just has one partition and
>that can be configured so that only permitted ELx is allowed to access
>it(in your case it's EL1)
>
Yes.

Thanks,
Lina