linux-kernel - Re: [PATCH 2/8] dt-bindings: clock: stm32mp1: describes clocks if "st,stm32mp1-rcc-secure"

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Date:   Tue, 26 Apr 2022 13:44:11 -0500
From:   Rob Herring <robh@...nel.org>
To:     Marek Vasut <marex@...x.de>
Cc:     Alexandre Torgue <alexandre.torgue@...s.st.com>, arnd@...db.de,
        Krzysztof Kozlowski <krzk+dt@...nel.org>, soc@...nel.org,
        Stephen Boyd <sboyd@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-kernel@...r.kernel.org,
        Ahmad Fatoum <a.fatoum@...gutronix.de>, etienne.carriere@...com
Subject: Re: [PATCH 2/8] dt-bindings: clock: stm32mp1: describes clocks if
 "st,stm32mp1-rcc-secure"

On Mon, Apr 25, 2022 at 09:35:13PM +0200, Marek Vasut wrote:
> On 4/25/22 21:11, Rob Herring wrote:
> > On Fri, Apr 22, 2022 at 06:31:25PM +0200, Marek Vasut wrote:
> > > On 4/22/22 17:09, Alexandre Torgue wrote:
> > > > In case of "st,stm32mp1-rcc-secure" (stm32mp1 clock driver with RCC
> > > > security support hardened), "clocks" and "clock-names" describe oscillators
> > > > and are required.
> > > > 
> > > > Signed-off-by: Alexandre Torgue <alexandre.torgue@...s.st.com>
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/clock/st,stm32mp1-rcc.yaml b/Documentation/devicetree/bindings/clock/st,stm32mp1-rcc.yaml
> > > > index 7a251264582d..bb0e0b92e907 100644
> > > > --- a/Documentation/devicetree/bindings/clock/st,stm32mp1-rcc.yaml
> > > > +++ b/Documentation/devicetree/bindings/clock/st,stm32mp1-rcc.yaml
> > > > @@ -58,14 +58,8 @@ properties:
> > > >              - st,stm32mp1-rcc-secure
> > > >              - st,stm32mp1-rcc
> > > >          - const: syscon
> > > > -
> > > > -  clocks:
> > > > -    description:
> > > > -      Specifies the external RX clock for ethernet MAC.
> > > > -    maxItems: 1
> > > > -
> > > > -  clock-names:
> > > > -    const: ETH_RX_CLK/ETH_REF_CLK
> > > > +  clocks: true
> > > > +  clock-names: true
> > > 
> > > It looks like this should rather be a property than a compatible string --
> > > the compatible string is used by the OS to determine which hardware is
> > > represented by a node, but here it is the same hardware in either case,
> > > "st,stm32mp1-rcc" and "st,stm32mp1-rcc-secure", it is still the same
> > > STM32MP1 RCC block, just configured differently by some bootloader stage.
> > > 
> > > So why not just add one-liner property of the RCC block like ?
> > > st,rcc-in-secure-configuration
> > 
> > Because using compatible was already decided.
> 
> I see ... may I ask why compatible is OK in this case even though this is
> encoding a policy (secure/non-secure configuration of the same clock IP)
> into DT ?

I see 'compatible' as an encoding of what is the programming model of 
the device. Secure vs. non-secure have different models. PCIe hosts vs 
endpoint mode is a similar case where we mostly have 2 compatibles (but 
not always).

I wouldn't say which way we do things is set in stone, but in this case 
we already decided something.

Rob