linux-kernel - Re: [PATCH 17/24] arm64: dts: qcom: glymur-crd: Avoid RTC probe failure

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Message-ID: <20251013110407.dqpjdrdaw4gzpcy4@hu-kamalw-hyd.qualcomm.com>
Date: Mon, 13 Oct 2025 16:34:07 +0530
From: Kamal Wadhwa <kamal.wadhwa@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
        Pankaj Patil <pankaj.patil@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 17/24] arm64: dts: qcom: glymur-crd: Avoid RTC probe
 failure

On Mon, Oct 06, 2025 at 04:28:59PM +0200, Konrad Dybcio wrote:
> On 10/1/25 2:23 PM, Kamal Wadhwa wrote:
> > Hi Krzysztof,
> > 
> > On Thu, Sep 25, 2025 at 1:41 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:
> >>
> >> On Thu, 25 Sept 2025 at 15:34, Pankaj Patil
> >> <pankaj.patil@....qualcomm.com> wrote:
> >>>
> >>> From: Kamal Wadhwa <kamal.wadhwa@....qualcomm.com>
> >>>
> >>> On Glymur boards, the RTC alarm interrupts are routed to SOCCP
> >>> subsystems and are not available to APPS. This can cause the
> >>> RTC probe failure as the RTC IRQ registration will fail in
> >>> probe.
> >>>
> >>> Fix this issue by adding `no-alarm` property in the RTC DT
> >>> node. This will skip the RTC alarm irq registration and
> >>> the RTC probe will return success.
> >>
> >>
> >> This is ridiculous. You just added glymur CRD and you claim now that
> >> it's broken and you need to fix it. So just fix that commit!
> > 
> > I'm afraid, but this is an actual limitation we have for Glymur
> > (compared to Kaanapali).
> > The RTC is part of the pmk8850.dtsi that is common between Kaanapali and
> > Glymur. On Glymur (unlike Kaanapali) the APPS processor does *not* have the RTC
> > IRQ permission for the RTC peripheral.
> 
> This is interesting.. is that a physical limitation, or some sort of
> a software security policy?

This is mostly a limitation for all compute targets(like Glymur). On compute
targets we need to support ACPI TAD feature[1] this feature uses the RTC alarm.
In a nutshell, this feature implements 2 times - AC ( adaptor power) and
DC (battery power) timers, and based on active power source(AC or DC?) at the
time of timer expiry device will either go for a full bootup or stay in power
down.

This feature is implemented on a different subsystem (SoCCP subsystem), and
since the SPMI `IRQ` permissions can only be assigned to only one subsystem,
so we can't use the alarms on APPS. This is why we use no-alarms DT to register
RTC device without alarm-irq support.

[1] TAD specification - https://uefi.org/sites/default/files/resources/ACPI_5.pdf
section 9.18

Regards,
Kamal