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 17:42:58 +0100
From: Conor Dooley <conor@...nel.org>
To: Serge Semin <fancer.lancer@...il.com>
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 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

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