linux-kernel - Re: [PATCH/RFC v4 2/4] regulator: fixed: add regulator

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Message-ID: <20200629172651.GG5499@sirena.org.uk>
Date:   Mon, 29 Jun 2020 18:26:51 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "magnus.damm@...il.com" <magnus.damm@...il.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH/RFC v4 2/4] regulator: fixed: add regulator_ops members
 for suspend/resume

On Mon, Jun 29, 2020 at 05:42:07PM +0100, Sudeep Holla wrote:
> On Mon, Jun 29, 2020 at 05:14:50PM +0100, Mark Brown wrote:
> > On Mon, Jun 29, 2020 at 04:07:28PM +0100, Sudeep Holla wrote:
> >
> > > The specification states clearly:
> > > "... all devices in the system must be in a state that is compatible
> > > with entry into the system state. These preconditions are beyond the scope
> > > of this specification and are therefore not described here."
> > > "Prior to the call, the OS must disable all sources of wakeup other than
> > > those it needs to support for its implementation of suspend to RAM."

> > This gets a bit circular for a generic OS since the OS needs some way to
> > figure out what it's supposed to do on a given platform - for example
> > the OS may be happy to use wakeup sources that the firmware is just
> > going to cut power on.

> While I understand the sentiments here, PSCI is targeted to address CPU
> power state management mainly and system states like suspend/reset and
> poweroff which involves last CPU. This is one of the reason it is out of
> the scope of the specification.

Sure, but as soon as we start talking about the last CPU stuff we're
inevitably talking about the system as a whole.

> Here is my understanding. DT specifies all the wakeup sources. Linux
> can configure those and user may choose to enable a subset of them is
> wakeup. As stated in the spec and also based on what we already do in
> the kernel, we disable all other wakeup sources.

> The PSCI firmware can then either read those from the interrupt controller
> or based on static platform understanding, must not disable those wakeup
> sources.

That bit about static platform understanding isn't super helpful for the
OS, so long as the firmware might do that the OS is pretty much out of
luck.  

> > > I see nothing has been fixed in the firmware too and we are still
> > > discussing the same after 3 years 😄. Clearly we should start trusting
> > > firmware and built capability to fix and replace it if there are bugs
> > > just like kernel and stop hacking around in the kernel to deal with
> > > just broken platform/psci firmware.

> > This isn't just an issue of buggy firmware as far as I can see, it's
> > also a lack of ability for the OS and firmware to communicate
> > information about their intentions to each other.  As things stand you'd
> > need to put static information in the DT.

> It is easy for DT to get out of sync with firmware unless it is generated
> by the same firmware. That's the reason why I am against such multiple

The ability for things to get out of sync also concerns me as I said
further back in the thread but I'm not sure we have much alternative,
realistically we're going to need some facility to work around firmware
that isn't ideal.

> sources of information. I understand ACPI has more flexibility and I did

ACPI has a much stronger idea of what the system looks like which helps
it a lot here.

> Each device or platform having its specific property in DT is not scalable.
> Not sure if it is a generic problem. If it is, I would like to understand
> more details on such lack of ability for communtication between OS and
> firmware.

It seems like a generic issue from where I'm sitting.

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