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

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Date:   Wed, 24 Jan 2018 10:10:35 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Lina Iyer <ilina@...eaurora.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        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 23/01/18 18:44, Lina Iyer wrote:
> On Tue, Jan 23 2018 at 18:15 +0000, Sudeep Holla wrote:
>> Hi Lina,
>>
>> On Tue, Jan 23, 2018 at 5:56 PM, Lina Iyer <ilina@...eaurora.org> wrote:
>>> On newer Qualcomm Techonologies Inc's SoCs like the SDM845, the GIC
>>> is in a
>>> power domain that can be powered off when not needed. Interrupts that
>>> need to
>>> be sensed even when the GIC is powered off, are routed through an
>>> interrupt
>>> controller in an always-on domain called the Power Domain Controller
>>> a.k.a PDC.
>>> This series adds support for the PDC's interrupt controller.
>>>
>>
>> Sorry for the basic questions:
>>
>> 1. Will the GIC be powered off in any other state other than System
>> suspend ?
>>
> Yes. When all the CPUs are in idle, there is an opportunity to power off
> the CPU's power domain and the GIC. QCOM SoCs have been doing that for
> many generations now.
> 

OK interesting, in that case so either GIC state is saved/restored with
some out of tree patches or the firmware takes care of it and it's
transparent to Linux ?

Also when will this PDC wakeup interrupts get configured ?

>> 2. Why this needs to be done in Linux, why can't it be transparent and
>> hidden
>>    in the firmware doing the actual GIC power down ? I assume Linux is
>> not
>>    powering down the GIC.
> No. You are right, Linux is not powering off the GIC directly. A
> dedicated processor for power management in the SoC does that. Platform
> drivers in Linux, know and configure the wakeup interrupts (depending on
> the usecase). This is runtime specific and this is the way to tell the
> SoC to wake up the processor even if the GIC and the CPU domain were
> powered off.
> 

OK, understood. By transparent, I mean firmware can copy the interrupts
enabled in the GIC to the PDC. It need not be kernel driven.

>>
>> 3. I see some bits that enable secure interrupts in one of the patch.
>> Is that even
>>    safe to allow Linux to enable some secure interrupts in PDC ?
>>
> Linux should not and would not configure secure interrupts. We would not
> have permissions for secure interrupts. The interrupt names might be a
> misnomer, but the interrupts listed in patch #4 are all non-secure
> interrupts.
> 

OK. So I can assume PDC is partitioned in secure and non-secure. If not
it's safe not have any access for PDC in the kernel. Couple of designs
of similar PDC I have seen is system wide and does handle even secure
part of the system. That was the main reason for checking.

-- 
Regards,
Sudeep