linux-kernel - Re: [PATCH 3/5] dt-bindings: reset: ocelot: Add documentation for 'microchip,reset-switch-core' property

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Message-ID: <871rjnxm5h.fsf@soft-dev15.microsemi.net>
Date:   Mon, 31 Aug 2020 10:19:38 +0200
From:   Lars Povlsen <lars.povlsen@...rochip.com>
To:     Sebastian Reichel <sre@...nel.org>
CC:     Lars Povlsen <lars.povlsen@...rochip.com>,
        Rob Herring <robh@...nel.org>, SoC Team <soc@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        <linux-pm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/5] dt-bindings: reset: ocelot: Add documentation for 'microchip,reset-switch-core' property


Sebastian Reichel writes:

> Hi,
> 
> On Tue, Jun 02, 2020 at 11:49:08AM +0200, Lars Povlsen wrote:
> > Rob Herring writes:
> > > On Wed, May 13, 2020 at 03:08:40PM +0200, Lars Povlsen wrote:
> > >> This documents the 'microchip,reset-switch-core' property in the
> > >> ocelot-reset driver.
> > >>
> > >> Signed-off-by: Lars Povlsen <lars.povlsen@...rochip.com>
> > >> ---
> > >>  .../devicetree/bindings/power/reset/ocelot-reset.txt        | 6 ++++++
> > >>  1 file changed, 6 insertions(+)
> > >>
> > >> diff --git a/Documentation/devicetree/bindings/power/reset/ocelot-rese=
> t.txt b/Documentation/devicetree/bindings/power/reset/ocelot-reset.txt
> > >> index 4d530d8154848..20fff03753ad2 100644
> > >> --- a/Documentation/devicetree/bindings/power/reset/ocelot-reset.txt
> > >> +++ b/Documentation/devicetree/bindings/power/reset/ocelot-reset.txt
> > >> @@ -9,9 +9,15 @@ microchip Sparx5 armv8 SoC's.
> > >>  Required Properties:
> > >>   - compatible: "mscc,ocelot-chip-reset" or "microchip,sparx5-chip-res=
> et"
> > >>
> > >> +Optional properties:
> > >> +- microchip,reset-switch-core : Perform a switch core reset at the
> > >> +  time of driver load. This is may be used to initialize the switch
> > >> +  core to a known state (before other drivers are loaded).
> > >
> > > How do you know when other drivers are loaded? This could be a module
> > > perhaps. Doesn't seem like something that belongs in DT.
> > >
> > 
> > The reset driver is loaded at postcore_initcall() time, which ensures it
> > is loaded before other drivers using the switch core. I noticed other
> > drivers do the same to do low-level system reset and initialization at
> > early boot time.
> > 
> > > Can this behavior be implied with "microchip,sparx5-chip-reset"?
> > 
> > Since we need to cater for both modus operandi, I would need two driver
> > compatible strings per platform, which scales worse than a single
> > property.
> > 
> > The "microchip,reset-switch-core" is a device configuration property
> > which tells the system (driver) how the hw should be handled. Since you
> > do not *always* want to reset the switch core (f.ex. when implementing
> > systems with warm reboot), I think it makes perfect sense - but I may be
> > biased off course :-)
> > 
> > Thank you for (all) of your comments, by the way!
> > 
> > ---Lars
> > > Rob
> 
> Is this series still needed? Did I miss a follow-up?

Hi Sebastian!

Yes, the series is still needed, but the conversation died after my
last message.

If the DT-controlled reset property is too controversial, I am willing
to drop that part. (Rob just reviewed the bindings).

MCHP reference designs have GPIO resets, so we *could* get by without,
but new designs may this feature.

> -- Sebastian

---Lars

-- 
Lars Povlsen,
Microchip