linux-kernel - Re: [PATCH 1/3] dt-bindings: mfd: Document the RTC present on MAX77620

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Date:   Fri, 1 May 2020 15:53:09 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Jon Hunter <jonathanh@...dia.com>, devicetree@...r.kernel.org,
        "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" 
        <linux-rtc@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] dt-bindings: mfd: Document the RTC present on
 MAX77620

On 01/05/2020 08:00:11-0500, Rob Herring wrote:
> > I don't think this is true because in the case of a discrete RTC, its
> > interrupt pin can be connected directly to a PMIC to power up a board
> > instead of being connected to the SoC. In that case we don't have an
> > interrupt property but the RTC is still a wakeup source. This is the
> > usual use case for wakeup-source in the RTC subsystem. Else, if there is
> > an interrupt, then we assume the RTC is a wakeup source and there is no
> > need to have the wakeup-source property.
> 
> Yes, that would be an example of "unless the wakeup mechanism is
> somehow not an interrupt". I guess I should add not an interrupt from
> the perspective of the OS.
> 
> So if the wakeup is self contained within the PMIC, why do we need a
> DT property? The capability is always there and enabling/disabling
> wakeup from it is userspace policy.
> 

Yes, for this particular case, I'm not sure wakeup-source is actually
necessary. If the interrupt line is used to wakeup the SoC, then the
presence of the interrupts property is enough to enable wakeup.

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com