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

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Date:   Tue, 2 Jun 2020 11:49:08 +0200
From:   Lars Povlsen <lars.povlsen@...rochip.com>
To:     Rob Herring <robh@...nel.org>
CC:     Lars Povlsen <lars.povlsen@...rochip.com>,
        Sebastian Reichel <sre@...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


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-reset.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-reset"
>>
>> +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

-- 
Lars Povlsen,
Microchip