linux-kernel - Re: [PATCH 06/17] dt-bindings: net: mscc-miim: Add resets property

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Date: Tue, 30 Apr 2024 17:40:23 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Thomas Gleixner <tglx@...utronix.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, Lee Jones <lee@...nel.org>, Arnd Bergmann
 <arnd@...db.de>, Horatiu Vultur <horatiu.vultur@...rochip.com>,
 UNGLinuxDriver@...rochip.com, Heiner Kallweit <hkallweit1@...il.com>,
 Russell King <linux@...linux.org.uk>, Saravana Kannan
 <saravanak@...gle.com>, Bjorn Helgaas <bhelgaas@...gle.com>, Philipp Zabel
 <p.zabel@...gutronix.de>, Lars Povlsen <lars.povlsen@...rochip.com>, Steen
 Hegelund <Steen.Hegelund@...rochip.com>, Daniel Machon
 <daniel.machon@...rochip.com>, Alexandre Belloni
 <alexandre.belloni@...tlin.com>, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, netdev@...r.kernel.org,
 linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, Allan
 Nielsen <allan.nielsen@...rochip.com>, Luca Ceresoli
 <luca.ceresoli@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 06/17] dt-bindings: net: mscc-miim: Add resets property

Hi Andrew,

On Tue, 30 Apr 2024 15:55:58 +0200
Andrew Lunn <andrew@...n.ch> wrote:

> On Tue, Apr 30, 2024 at 10:37:15AM +0200, Herve Codina wrote:
> > Add the (optional) resets property.
> > The mscc-miim device is impacted by the switch reset especially when the
> > mscc-miim device is used as part of the LAN966x PCI device.
> > 
> > Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> > ---
> >  Documentation/devicetree/bindings/net/mscc,miim.yaml | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/net/mscc,miim.yaml b/Documentation/devicetree/bindings/net/mscc,miim.yaml
> > index 5b292e7c9e46..a8c92cec85a6 100644
> > --- a/Documentation/devicetree/bindings/net/mscc,miim.yaml
> > +++ b/Documentation/devicetree/bindings/net/mscc,miim.yaml
> > @@ -38,6 +38,14 @@ properties:
> >  
> >    clock-frequency: true
> >  
> > +  resets:
> > +    items:
> > +      - description: Reset controller used for switch core reset (soft reset)  
> 
> A follow up to the comment on the next patch. I think it should be
> made clear in the patch and the binding, the aim is to reset the MDIO
> bus master, not the switch. It just happens that the MDIO bus master
> is within the domain of the switch core, and so the switch core reset
> also resets the MDIO bus master.

Exactly.

> 
> Architecturally, this is important. I would not expect the MDIO driver
> to be resetting the switch, the switch driver should be doing
> that. But we have seen some odd Qualcomm patches where the MDIO driver
> has been doing things outside the scope of MDIO, playing with resets
> and clocks which are not directly related to the MDIO bus master. I
> want to avoid any confusion here, especially when Qualcomm tries
> again, and maybe points at this code.
> 

Sure.

We have the same construction with the pinctrl driver used in the LAN966x
  Documentation/devicetree/bindings/pinctrl/mscc,ocelot-pinctrl.yaml

The reset name is 'switch' in the pinctrl binding.
I can use the same description here as the one present in the pinctrl binding:
  description: Optional shared switch reset.
and keep 'switch' as reset name here (consistent with pinctrl reset name).

What do you think about that ?

Best regards,
Hervé

-- 
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com