linux-kernel - Re: [PATCH 2/2] dt-bindings: net: dsa: qca8k: Add PORT0_PAD

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Date:   Mon, 20 Jul 2020 19:59:30 -0600
From:   Rob Herring <robh@...nel.org>
To:     Matthew Hagan <mnhagan88@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>, linux@...linux.org.uk,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        John Crispin <john@...ozen.org>,
        Jonathan McDowell <noodles@...th.li>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 2/2] dt-bindings: net: dsa: qca8k: Add PORT0_PAD_CTRL
 properties

On Fri, Jul 17, 2020 at 08:26:02PM +0100, Matthew Hagan wrote:
> 
> 
> On 16/07/2020 23:32, Andrew Lunn wrote:
> > On Thu, Jul 16, 2020 at 03:09:25PM -0700, Jakub Kicinski wrote:
> >> On Mon, 13 Jul 2020 21:50:26 +0100 Matthew Hagan wrote:
> >>> Add names and decriptions of additional PORT0_PAD_CTRL properties.
> >>>
> >>> Signed-off-by: Matthew Hagan <mnhagan88@...il.com>
> >>> ---
> >>>  Documentation/devicetree/bindings/net/dsa/qca8k.txt | 8 ++++++++
> >>>  1 file changed, 8 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/net/dsa/qca8k.txt b/Documentation/devicetree/bindings/net/dsa/qca8k.txt
> >>> index ccbc6d89325d..3d34c4f2e891 100644
> >>> --- a/Documentation/devicetree/bindings/net/dsa/qca8k.txt
> >>> +++ b/Documentation/devicetree/bindings/net/dsa/qca8k.txt
> >>> @@ -13,6 +13,14 @@ Optional properties:
> >>>  
> >>>  - reset-gpios: GPIO to be used to reset the whole device
> >>>  
> >>> +Optional MAC configuration properties:
> >>> +
> >>> +- qca,exchange-mac0-mac6:	If present, internally swaps MAC0 and MAC6.
> >>
> >> Perhaps we can say a little more here?
> >>
> >>> +- qca,sgmii-rxclk-falling-edge:	If present, sets receive clock phase to
> >>> +				falling edge.
> >>> +- qca,sgmii-txclk-falling-edge:	If present, sets transmit clock phase to
> >>> +				falling edge.
> >>
> >> These are not something that other vendors may implement and therefore
> >> something we may want to make generic? Andrew?
> > 
> > I've never seen any other vendor implement this. Which to me makes me
> > think this is a vendor extension, to Ciscos vendor extension of
> > 1000BaseX.
> > 
> > Matthew, do you have a real use cases of these? I don't see a DT patch
> > making use of them. And if you do, what is the PHY on the other end
> > which also allows you to invert the clocks?
> > 
> The use case I am working on is the Cisco Meraki MX65 which requires bit
> 18 set (qca,sgmii-txclk-falling-edge). On the other side is a BCM58625
> SRAB with ports 4 and 5 in SGMII mode. There is no special polarity
> configuration set on this side though I do have very limited info on
> what is available. The settings I have replicate the vendor
> configuration extracted from the device.
> 
> The qca,sgmii-rxclk-falling-edge option (bit 19) is commonly used
> according to the device trees found in the OpenWrt, which is still using
> the ar8216 driver. With a count through the ar8327-initvals I see bit 19
> set on 18 of 22 devices using SGMII on MAC0.

Can't you identify the device and configure the setting based on that? 
After all, MDIO devices are discoverable. Or there's no MDIO here?

Rob