linux-kernel - Re: [PATCH net-next v3 06/10] dt-bindings: net: Add Synopsys DW xPCS bindings

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Date: Fri, 28 Jun 2024 20:06:21 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Conor Dooley <conor@...nel.org>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, 
	Russell King <linux@...linux.org.uk>, Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	Jose Abreu <joabreu@...opsys.com>, Jose Abreu <Jose.Abreu@...opsys.com>, 
	Vladimir Oltean <olteanv@...il.com>, Florian Fainelli <f.fainelli@...il.com>, 
	Maxime Chevallier <maxime.chevallier@...tlin.com>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.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>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Sagar Cheluvegowda <quic_scheluve@...cinc.com>, 
	Abhishek Chauhan <quic_abchauha@...cinc.com>, Andrew Halaney <ahalaney@...hat.com>, 
	Jiawen Wu <jiawenwu@...stnetic.com>, Mengyuan Lou <mengyuanlou@...-swift.com>, 
	Tomer Maimon <tmaimon77@...il.com>, openbmc@...ts.ozlabs.org, netdev@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 06/10] dt-bindings: net: Add Synopsys DW xPCS
 bindings

On Fri, Jun 28, 2024 at 05:42:58PM +0100, Conor Dooley wrote:
> On Thu, Jun 27, 2024 at 08:10:48PM +0300, Serge Semin wrote:
> > On Thu, Jun 27, 2024 at 04:51:22PM +0100, Conor Dooley wrote:
> > > On Thu, Jun 27, 2024 at 03:41:26AM +0300, Serge Semin wrote:
> > > > +  clocks:
> > > > +    description:
> > > > +      Both MCI and APB3 interfaces are supposed to be equipped with a clock
> > > > +      source connected via the clk_csr_i line.
> > > > +
> > > > +      PCS/PMA layer can be clocked by an internal reference clock source
> > > > +      (phyN_core_refclk) or by an externally connected (phyN_pad_refclk) clock
> > > > +      generator. Both clocks can be supplied at a time.
> > > > +    minItems: 1
> > > > +    maxItems: 3
> > > > +
> > > > +  clock-names:
> > > > +    oneOf:
> > > > +      - minItems: 1
> > > > +        items:
> > > > +          - enum: [core, pad]
> > > > +          - const: pad
> > > > +      - minItems: 1
> > > > +        items:
> > > > +          - const: pclk
> > > > +          - enum: [core, pad]
> > > > +          - const: pad
> > > 
> > 
> > > While reading this, I'm kinda struggling to map "clk_csr_i" to a clock
> > > name. Is that pclk? And why pclk if it is connected to "clk_csr_i"?
> > 
> > Right. It's "pclk". The reason of using the "pclk" name is that it has
> > turned to be a de-facto standard name in the DT-bindings for the
> > peripheral bus clock sources utilized for the CSR-space IO buses.
> > Moreover the STMMAC driver responsible for the parental DW *MAC
> > devices handling also has the "pclk" name utilized for the clk_csr_i
> > signal. So using the "pclk" name in the tightly coupled devices (MAC
> > and PCS) for the same signal seemed a good idea.
> > 
> > > If two interfaces are meant to be "equipped" with that clock, how come
> > > it is optional? I'm probably missing something...
> > 
> > MCI and APB3 interfaces are basically the same from the bindings
> > pointer of view. Both of them can be utilized for the DW XPCS
> > installed on the SoC system bus, so the device could be accessed using
> > the simple MMIO ops.
> > 
> > The first "clock-names" schema is meant to be applied on the DW XPCS
> > accessible over an _MDIO_ bus, which obviously doesn't have any
> > special CSR IO bus. In that case the DW XPCS device is supposed to be
> > defined as a subnode of the MDIO-bus DT-node.
> > 
> > The second "clock-names" constraint is supposed to be applied to the
> > DW XPCS synthesized with the MCI/APB3 CSRs IO interface. The device in
> > that case should be defined in the DT source file as a normal memory
> > mapped device.
> > 
> > > 
> > > Otherwise this binding looks fine to me.
> > 
> > Shall I add a note to the clock description that the "clk_csr_i"
> > signal is named as "pclk"? I'll need to resubmit the series anyway.
>
 
> Better yet, could you mention MDIO? It wasn't clear to me (but I'm just
> reviewing bindings not a dwmac-ist) that MCI and APB3 were only two of
> the options and that the first clock-names was for MDIO. Maybe something
> like:
> 
>   clock-names:
>     oneOf:
>       - minItems: 1
>         items: # MDIO
>           - enum: [core, pad]
>           - const: pad
>       - minItems: 1
>         items: # MCI or APB
>           - const: pclk
>           - enum: [core, pad]
>           - const: pad

Agreed. I'll add the comments to the oneOf-subschemas as you
suggested.

Thanks,
-Serge(y)